3.4.21.B30 highly purified UmuD is specifically degraded in vitro by Lon protease in an ATP-dependent manner, UmuD' is insensitive to proteolysis by Lon 651420 3.4.21.B30 highly purified UmuD/D' heterodimer is degraded in the presence of ATP, ClpP and ClpX, no degradation occurs when ClpX is omitted 650976 3.4.21.B30 UmuD/UmuD' heterodimer is more stable than each of the homodimers 651622