Letter to the Editor Letter to the Editor amino acid sequence identity and similarity amongst them-The Y-Family of DNA Polymerases UmuC/DinB/Rev1/Rad30 DNA polymerases be referred ESBS Boulevard S. Brant to as the "Y-family" of DNA polymerases.Phylogenetic analysis of the Y-family of DNA poly-67400 Strasbourg France merases reveals several branches to an unrooted tree (Figure 1). Interestingly, not all branches are evenly dis-

The REV3 and REV7 genes of the yeast Saccharomyces cerevisiae are required for DNA damage-induced mutagenesis. The Rev3 and Rev7 proteins were shown to form a complex with DNA polymerase activity. This polymerase replicated past a thymine-thymine cis-syn cyclobutane dimer, a lesion that normally severely inhibits replication, with an efficiency of approximately 10 percent. In contrast, bypass replication efficiency with yeast DNA polymerase alpha was no more than 1 percent. The Rev3-Rev7 complex is the sixth eukaryotic DNA polymerase to be described, and is therefore called DNA polymerase zeta.

Mutagenesis induced by DNA damage in Saccharomyces cerevisiae requires the products of the REV1, REV3 and REV7 genes. The Rev3 and Rev7 proteins are subunits of DNA polymerase-zeta (Pol-zeta), an enzyme whose sole function appears to be translesion synthesis. Rev1 protein has weak homology with UmuC protein which facilitates translesion synthesis in Escherichia coli by an unknown mechanism. We show here that Rev1 protein has a deoxycytidyl transferase activity which transfers a dCMP residue from dCTP to the 3' end of a DNA primer in a template-dependent reaction. Efficient transfer occurred opposite a template abasic site, but approximately 20% transfer also occurred opposite a template guanine and approximately 10% opposite adenine or uracil; < or = 1% was seen opposite thymine or cytosine. Insertion of cytosine opposite an abasic site produced a terminus that was extended efficiently by Pol-zeta, but not by yeast Pol-alpha.

No abstract

SummaryThe function of the Saccharomyces cerevisiae REV1 gene is required for translesion replication and mutagenesis induced by a wide variety of DNAdamaging agents. We showed previously that Rev1p possesses a deoxycytidyl transferase activity, which incorporates dCMP opposite abasic sites in the DNA template, and that dCMP insertion is the major event during bypass of an abasic site in vivo. However, we now find that Rev1p function is needed for the bypass of a T±T (6±4) UV photoproduct, a process in which dCMP incorporation occurs only very rarely, indicating that Rev1p possesses a second function. In addition, we find that Rev1p function is, as expected, required for bypass of an abasic site. However, replication past this lesion was also much reduced in the G-193R rev1-1 mutant, which we find retains substantial levels of deoxycytidyl transferase activity. This mutant is, therefore, presumably deficient principally in the second, at present poorly defined, function. The bypass of an abasic site and T±T (6±4) lesion also depended on REV3 function, but neither it nor REV1 was required for replication past the T±T dimer; bypass of this lesion presumably depends on another enzyme.