6.3.3.1 - 1307, 1317 6.3.3.1 cloning and characterization of a 12-gene cluster encoding nine enzymes for de novo purine nucleotide synthesis. The cluster is likely an operon and is organized into three groups of overlapping genes followed by the last gene: purEKB-purC(or)QLF-purMNH(J)-purD 1259 6.3.3.1 expression in Escherichia coli 1306 6.3.3.1 expression in Escherichia coli of a histidine-tagged enzyme 651681 6.3.3.1 expression in Escherichia coli of a histidine-tagged recombinant enzyme 653485 6.3.3.1 expression in Saccharomyces cerevisiae 653875 6.3.3.1 expression of recombinant enzymes in Escherichia coli 649909 6.3.3.1 expression of the trifunctional enzyme with AIR synthetase activity, phosphoribosylglycinamide synthetase activity, and phosphoribosylglycinamide transformylase activity, in mutant CHO cells 1318