Literature summary extracted from

V�rtler, S.; M�rl, M.
tRNA-nucleotidyltransferases: Highly unusual RNA polymerases with vital functions (2010), FEBS Lett., 584, 297-302.

Protein Variants

EC Number	Protein Variants	Comment	Organism
2.7.7.72	additional information	replacement of the highly conserved residues glutamic acid, aspartic acid and arginine o f the EDxxR motif aabolishes nucleotide specificity of the enzyme	Escherichia coli
2.7.7.72	additional information	replacement of the highly conserved residues glutamic acid, aspartic acid and arginine o f the EDxxR motif aabolishes nucleotide specificity of the enzyme	Homo sapiens

Metals/Ions

EC Number	Metals/Ions	Comment	Organism
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Thermus thermophilus
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Escherichia coli
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Homo sapiens
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Archaea
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Deinococcus radiodurans
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Aquifex aeolicus
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Halalkalibacterium halodurans
2.7.7.72	Mg2+	essentially required, two metal ions are coordinated by highly conserved carboxylates and fulfill specific roles in catalyzing the reaction. Metal ion A activates the 3'-hydroxyl group of the primer for a nucleophilic in-line attack on the alpha-phosphate of the incoming NTP, while metal ion B promotes the leaving of the diphosphate group that is released during this reaction	Caldanaerobacter subterraneus subsp. tengcongensis
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Thermus thermophilus
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Escherichia coli
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Homo sapiens
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Archaea
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Deinococcus radiodurans
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Aquifex aeolicus
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Halalkalibacterium halodurans
2.7.7.72	additional information	Mn2+ cannot substitute for Mg2+	Caldanaerobacter subterraneus subsp. tengcongensis

Natural Substrates/ Products (Substrates)

EC Number	Natural Substrates	Organism	Comment (Nat. Sub.)	Natural Products	Comment (Nat. Pro.)	Rev.
2.7.7.72	additional information	Thermus thermophilus	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Escherichia coli	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Homo sapiens	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Archaea	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Deinococcus radiodurans	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Aquifex aeolicus	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Halalkalibacterium halodurans	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?
2.7.7.72	additional information	Caldanaerobacter subterraneus subsp. tengcongensis	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	?	-	?

Organism

EC Number	Organism	UniProt	Comment	Textmining
2.7.7.72	Aquifex aeolicus	-	-	-
2.7.7.72	Archaea	-	-	-
2.7.7.72	Caldanaerobacter subterraneus subsp. tengcongensis	-	-	-
2.7.7.72	Deinococcus radiodurans	-	-	-
2.7.7.72	Escherichia coli	-	-	-
2.7.7.72	Halalkalibacterium halodurans	-	-	-
2.7.7.72	Homo sapiens	-	-	-
2.7.7.72	Thermus thermophilus	-	-	-

Substrates and Products (Substrate)

EC Number	Substrates	Comment Substrates	Organism	Products	Comment (Products)	Rev.
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Thermus thermophilus	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Escherichia coli	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Homo sapiens	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Archaea	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Deinococcus radiodurans	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Aquifex aeolicus	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Halalkalibacterium halodurans	?	-	?
2.7.7.72	additional information	the specific enzyme incorporates only a highly restricted number of nucleotides in a tRNA primer and then stops polymerization at a high efficiency and accuracy. It selects exclusively CTP and ATP for incorporation and discriminates strongly against the other two nucleotide triphosphates. It does not require a nucleic acid template for directing order and nature of nucleotides to be inserted and is highly selective for tRNA-like structures as a polymerization substrate. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Caldanaerobacter subterraneus subsp. tengcongensis	?	-	?
2.7.7.72	additional information	class 1 enzymes recognize and select the correct nucleotides not as pure protein-based enzymes, but as ribonucleoproteins, where the tRNA part is not just a substrate molecule (primer), but is an active part of the nucleotide binding pocket	Archaea	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Thermus thermophilus	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Escherichia coli	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Homo sapiens	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Deinococcus radiodurans	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Aquifex aeolicus	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Halalkalibacterium halodurans	?	-	?
2.7.7.72	additional information	class 2 enzymes select the nucleotides to be incorporated by a true amino acid template that consists of the three highly conserved residues glutamic acid, aspartic acid and arginine (EDxxR). The arginine residue forms hydrogen bonds with ATP (1 bond) and CTP (2 bonds), assisted by aspartate that contributes one hydrogen bond	Caldanaerobacter subterraneus subsp. tengcongensis	?	-	?

Subunits

EC Number	Subunits	Comment	Organism
2.7.7.72	More	class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements, structure-function relationship, overview	Archaea
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Thermus thermophilus
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Escherichia coli
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Homo sapiens
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Deinococcus radiodurans
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Aquifex aeolicus
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Halalkalibacterium halodurans
2.7.7.72	More	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Caldanaerobacter subterraneus subsp. tengcongensis

Synonyms

EC Number	Synonyms	Comment	Organism
2.7.7.72	CCA-adding enzyme	-	Thermus thermophilus
2.7.7.72	CCA-adding enzyme	-	Escherichia coli
2.7.7.72	CCA-adding enzyme	-	Homo sapiens
2.7.7.72	CCA-adding enzyme	-	Archaea
2.7.7.72	CCA-adding enzyme	-	Deinococcus radiodurans
2.7.7.72	CCA-adding enzyme	-	Aquifex aeolicus
2.7.7.72	CCA-adding enzyme	-	Halalkalibacterium halodurans
2.7.7.72	CCA-adding enzyme	-	Caldanaerobacter subterraneus subsp. tengcongensis
2.7.7.72	class 1 tRNA-nucleotidyltransferase	-	Archaea
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Thermus thermophilus
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Escherichia coli
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Homo sapiens
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Deinococcus radiodurans
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Aquifex aeolicus
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Halalkalibacterium halodurans
2.7.7.72	class 2 tRNA-nucleotidyltransferase	-	Caldanaerobacter subterraneus subsp. tengcongensis

General Information

EC Number	General Information	Comment	Organism
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. Class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Thermus thermophilus
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. Class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Archaea
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. Class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Deinococcus radiodurans
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. Class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Aquifex aeolicus
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. Class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Halalkalibacterium halodurans
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. Class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Caldanaerobacter subterraneus subsp. tengcongensis
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. In class 2 enzymes, only the head domain carries a beta sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Escherichia coli
2.7.7.72	evolution	with a possible origin of ancient telomerase-like activity, the CCA-adding enzymes obviously emerged twice during evolution, leading to structurally different, but functionally identical enzymes. While the enzyme class 1 is exclusively found in archaea, class 2 tRNA-nucleotidyltransferases are present in eukaryotes and bacteria. In class 2 enzymes, only the head domain carries a beta sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure. The chemical mechanism underlying the polymerization appears conserved in all polymerases across the three kingdoms of life	Homo sapiens
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Thermus thermophilus
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Escherichia coli
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Homo sapiens
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Archaea
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Deinococcus radiodurans
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Aquifex aeolicus
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Halalkalibacterium halodurans
2.7.7.72	malfunction	CCA ends with misincorporated nucleotides are only rarely detected. Only under rather artificial in vitro conditions, e.g. in the presence of Mn2+ ions instead of Mg2+ or deviating NTP concentrations, incorporation of CCC as well as poly(C) tails can be observed	Caldanaerobacter subterraneus subsp. tengcongensis
2.7.7.72	additional information	class 1 enzymes have a tRNA-binding body domain consisting of a beta sheet with flanking alpha helices. Head and neck domains form the active site and are also composed of alpha-helical and beta-sheet elements, structure-function relationship, overview	Archaea
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Thermus thermophilus
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Escherichia coli
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Homo sapiens
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Deinococcus radiodurans
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Aquifex aeolicus
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Halalkalibacterium halodurans
2.7.7.72	additional information	in class 2 enzymes, only the head domain carries a beta-sheet and forms the nucleotidyltransferase core, while neck, body and tail consist exclusively of alpha helices, giving the enzyme a hook- or seahorse-like overall structure, structure-function relationship, overview	Caldanaerobacter subterraneus subsp. tengcongensis
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Thermus thermophilus
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Escherichia coli
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Homo sapiens
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Archaea
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Deinococcus radiodurans
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Aquifex aeolicus
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Halalkalibacterium halodurans
2.7.7.72	physiological function	tRNA-nucleotidyltransferases are RNA polymerases responsible for the synthesis of the nucleotide triplet CCA at the 3'-terminus of tRNAs. As this CCA end represents an essential functional element for aminoacylation and translation, the CCA-adding enzymes are of vital importance in all organisms. The enzyme fulfills both functions in maintenance/repair as well as de novo polymerization	Caldanaerobacter subterraneus subsp. tengcongensis