Polkappa is one of many DNA polymerases involved in translesion DNA synthesis (TLS). It belongs to the Y-family of polymerases along with Poleta, Poliota and hREV1. Unlike Poleta encoded by the xeroderma pigmentosum variant (XPV) gene, Polkappa is unable to bypass UV-induced DNA damage in vitro, but it is able to bypass benzo[a]pyrene (B[a]P)-adducted guanines accurately and efficiently. In an attempt to identify factor(s) targeting Polkappa to its cognate DNA lesion(s), we searched for Polkappa-interacting proteins by using the yeast two-hybrid assay. We found that Polkappa interacts with a C-terminal region of hREV1. Poleta and Poliota were also found to interact with the same region of hREV1. The interaction between Polkappa and hREV1 was confirmed by pull-down and co-immunoprecipitation assays. The C-terminal region of hREV1 is known to interact with hREV7, a non-catalytic subunit of Polzeta that is another structurally unrelated TLS enzyme, and we show that Polkappa and hREV7 bind to the same C-terminal region of hREV1. Thus, our results suggest that hREV1 plays a pivotal role in the multi-enzyme, multi-step process of translesion DNA synthesis.
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