title: Role of DNA polymerase eta in the bypass of a (6-4) TT photoproduct.
abstract: UV light-induced DNA lesions block the normal replication machinery. Eukaryotic cells possess DNA polymerase eta (Poleta), which has the ability to replicate past a cis-syn thymine-thymine (TT) dimer efficiently and accurately, and mutations in human Poleta result in the cancer-prone syndrome, the variant form of xeroderma pigmentosum. Here, we test Poleta for its ability to bypass a (6-4) TT lesion which distorts the DNA helix to a much greater extent than a cis-syn TT dimer. Opposite the 3' T of a (6-4) TT photoproduct, both yeast and human Poleta preferentially insert a G residue, but they are unable to extend from the inserted nucleotide. DNA Polzeta, essential for UV induced mutagenesis, efficiently extends from the G residue inserted opposite the 3' T of the (6-4) TT lesion by Poleta, and Polzeta inserts the correct nucleotide A opposite the 5' T of the lesion. Thus, the efficient bypass of the (6-4) TT photoproduct is achieved by the combined action of Poleta and Polzeta, wherein Poleta inserts a nucleotide opposite the 3' T of the lesion and Polzeta extends from it. These biochemical observations are in concert with genetic studies in yeast indicating that mutations occur predominantly at the 3' T of the (6-4) TT photoproduct and that these mutations frequently exhibit a 3' T-->C change that would result from the insertion of a G opposite the 3' T of the (6-4) TT lesion.
authors: Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston, Texas 77555-1061, USA.
authors: R E
authors: RE
authors: Johnson
authors: L
authors: L
authors: Haracska
authors: S
authors: S
authors: Prakash
authors: L
authors: L
authors: Prakash
mesh_terms: D000818:Animals; D004247:DNA / Q000235:genetics / Q000528:radiation effects; D004260:DNA Repair; D004259:DNA-Directed DNA Polymerase / Q000235:genetics*; D011740:Pyrimidine Dimers / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014466:Ultraviolet Rays
chemical_list: D011740:Pyrimidine Dimers; D004247:DNA; C425929:DNA polymerase zeta; D004259:DNA-Directed DNA Polymerase