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Effects of accessory proteins on the bypass of a cis-syn thymine-thymine dimer by Saccharomyces cerevisiae DNA polymerase η

Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Biochemistry (Impact Factor: 3.01). 08/2007; 46(30):8888-96. DOI: 10.1021/bi700234t
Source: PubMed

ABSTRACT Among several hypotheses to explain how translesion synthesis (TLS) by DNA polymerase eta (pol eta) suppresses ultraviolet light-induced mutagenesis in vivo despite the fact that pol eta copies DNA with low fidelity, here we test whether replication accessory proteins enhance the fidelity of TLS by pol eta. We first show that the single-stranded DNA binding protein RPA, the sliding clamp PCNA, and the clamp loader RFC slightly increase the processivity of yeast pol eta and its ability to recycle to new template primers. However, these increases are small, and they are similar when copying an undamaged template and a template containing a cis-syn TT dimer. Consequently, the accessory proteins do not strongly stimulate the already robust TT dimer bypass efficiency of pol eta. We then perform a comprehensive analysis of yeast pol eta fidelity. We show that it is much less accurate than other yeast DNA polymerases and that the accessory proteins have little effect on fidelity when copying undamaged templates or when bypassing a TT dimer. Thus, although accessory proteins clearly participate in pol eta functions in vivo, they do not appear to help suppress UV mutagenesis by improving pol eta bypass fidelity per se.

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    • "One possibility is that POLH-1 degradation is part of the mechanism that allows exchange of POLH-1 for the replicative polymerase after TLS. Current models for TLS suggest that post-TLS exchange occurs because pol eta, which exhibits low processivity in vitro (Washington et al., 1999; McCulloch et al., 2004, 2007), simply disassociates from the template after TLS, and this allows the replicative polymerase to regain access to the primed site. We propose that early embryos may employ a more active mechanism to remove POLH-1 from the template after TLS, and that this involves the CRL4-Cdt2 mediated proteolysis step that we have identified. "
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