Opposing regulation by Rev1 of DNA polymerase zeta activity on damaged versus undamaged DNA

The Rev1 deoxycytidyl transferase functions as a scaffold protein for DNA polymerase ζ (Pol ζ)-mediated translesion synthesis (TLS). Biochemical studies with yeast enzymes indicate that Rev1 plays a dual regulatory role in TLS, stimulating Pol ζ activity at sites of damage but inhibiting its activity on undamaged DNA. An evolutionary conserved N-terminal alpha-helical motif (M1), located 10–20 amino acids upstream of Rev1’s single BRCT domain, is required for the inhibitory activity of Rev1 on undamaged DNA. Mutations in the M1 motif result in a stimulation of Pol ζ replication activity on both undamaged and damaged DNA. Yeast cells carrying a REV1 mutant lacking the M1 motif show a four-fold increase in complex mutations without significantly affecting overall spontaneous mutation rates. A catalytically inactive mutant of Rev1 still exerts these regulatory functions. However, regulation requires that Rev1 and Pol ζ form a stable complex, and that this complex is coordinated by the replication clamp PCNA.