Mutations in the ubiquitin binding UBZ motif of DNA polymerase η do not impair its function in translesion synthesis during replication

Treatment of Saccharomyces cerevisiae cells with DNA-damaging agents elicits lysine 164-linked PCNA monoubiquitination by Rad6-Rad18. Recently, a number of ubiquitin (Ub) binding domains (UBDs) have been identified in translesion synthesis (TLS) DNA polymerases and it has been proposed that the UBD in a TLS polymerase affects its binding to Ub on PCNA and that this binding mode is indispensable for a TLS polymerase to access PCNA at the site of a stalled replication fork. To evaluate the contribution of the binding of UBDs to the Ub moiety on PCNA in TLS, we have examined the effects of mutations in the C,H, zinc binding motif and in the conserved D570 residue that lies in the a-helix portion of the UBZ domain of yeast Pol eta. We find that mutations in the C2H2 motif have no perceptible effect on UV sensitivity or UV mutagenesis, whereas a mutation of the D570 residue adversely affects Pol eta function. The stimulation of DNA synthesis by Pol eta with PCNA or Ub-PCNA was not affected by mutations in the C,H, motif or the D570 residue. These observations lead us to suggest that the binding of Ub on PCNA via its UBZ domain is not a necessary requirement for the ability of polymerase eta to function in TLS during replication.