Practice question

E. coli maintains three error-prone polymerases under SOS control: Pol II encoded by polB for restart after damage, Pol IV encoded by dinB, and Pol V encoded by umuC-umuD for translesion synthesis past lesions. These belong to B and Y families lacking intrinsic 3' to 5' proofreading exonuclease and possessing spacious active sites tolerant of bulky lesions but misinserting bases frequently. Pol I and Pol III are high-fidelity replicative enzymes with strong proofreading exonuclease not classified error-prone. Deletion of dinB and umuC reduces UV-induced mutagenesis drastically but increases sensitivity.