Abstract
Although mammals encode multiple family X DNA polymerases implicated in DNA repair, Saccharomyces cerevisiae has only one, DNA polymerase IV (pol IV). To better understand the repair functions of pol IV, here we characterize its biochemical properties. Like mammalian pol beta and pol lambda, but not pol mu, pol IV has intrinsic 5'-2-deoxyribose-5-phosphate lyase activity. Pol IV has low processivity and can fill short gaps in DNA. Unlike the case with pol beta and pol lambda, the gap-filling activity of pol IV is not enhanced by a 5'-phosphate on the downstream primer but is stimulated by a 5'-terminal synthetic abasic site. Pol IV incorporates rNTPs into DNA with an unusually high efficiency relative to dNTPs, a property in common with pol mu but not pol beta or pol lambda. Finally, pol IV is highly inaccurate, with an unusual error specificity indicating the ability to extend primer termini with limited homology. These properties are consistent with a possible role for pol IV in base excision repair and with its known role in non-homologous end joining of double strand breaks, perhaps including those with damaged ends.
Highlights
Pol shares most of the above-mentioned properties with pol , suggesting that pol may function in BER [10, 11]
Pol IV has highest homology to mammalian pol and, like pol , polymerase IV (pol IV) contains a BRCT domain followed by a coding sequence of unknown function that is rich in serine and proline residues
The results presented here indicate that yeast pol IV is a hybrid of its mammalian homologs
Summary
Pol generates single base deletions, especially in non-iterated sequence contexts, at a much higher rate than pol , indicating an ability to use template-primers with minimal base pairing homology These properties, in combination with a BRCT domain and the ability to physically and functionally interact with several proteins involved in NHEJ of double strand breaks in DNA [13, 14], implicate pol in NHEJ. Pol , but not pol , can promote end-joining accuracy during Ig recombination in cultured cells, and studies with pol knockout mice indicate that it participates in the rearrangement of immunoglobulin light chain genes in vivo These observations indicate that multiple family X members with somewhat different properties are used for the highly specialized DNA repair reactions that occur in mammals. The results presented here indicate that yeast pol IV is a hybrid of its mammalian homologs
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