The mutagenesis protein UmuC is a DNA polymerase activated by UmuD ', RecA, and SSB and is specialized for translesion replication

Replication of DNA lesions leads to the formation of mutations. In Escheric hia coil this process is regulated by the SOS stress response, and requires the mutagenesis proteins UmuC and UmuD', Analysis of translesion replicati on using a recently reconstituted in vitro system (Reuven, N. B., Tomer, G. , and Livneh, Z. (1998) Mol. Cell 2, 191-199) revealed that lesion bypass o ccurred with a UmuC fusion protein, UmuD', RecA, and SSB in the absence of added DNA polymerase, Further analysis revealed that UmuC was a DNA polymer ase (E. coli DNA polymerase V), with a weak polymerizing activity. Upon add ition of UmuD', RecA, and SSB, the UmuC DNA polymerase was greatly activate d, and replicated a synthetic abasic site with great efficiency (45% bypass in 6 min), 10-100-fold higher than E. coil DNA polymerases I, II, or III h oloenzyme, Analysis of bypass products revealed insertion of primarily dAMP (69%), and to a lesser degree dGMP (31%) opposite the abasic site. The Umu C104, mutant protein was defective both in lesion bypass and in DNA synthes is. These results indicate that UmuC is a UmuD'-, RecA-, and SSB-activated DNA polymerase, which is specialized for lesion bypass. UmuC is a member of a new family of DNA polymerases which are specialized for lesion bypass, a nd include the yeast RAD30 and the human XP-V genes, encoding DNA polymeras e eta.