Role of DNA polymerase η in the bypass of a (6-4) TT photoproduct

R. E. Johnson, L. Haracska, S. Prakash, L. Prakash

Research output: Contribution to journalArticlepeer-review

172 Scopus citations


UV light-induced DNA lesions block the normal replication machinery. Eukaryotic cells possess DNA polymerase η (Polη), which has the ability to replicate past a cis-syn thymine-thymine (TT) dimer efficiently and accurately, and mutations in human Polη result in the cancer-prone syndrome, the variant form of xeroderma pigmentosum. Here, we test Polη 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 Polη preferentially insert a G residue, but they are unable to extend from the inserted nucleotide. DNA Polζ, essential for UV induced mutagenesis, efficiently extends from the G residue inserted opposite the 3′ T of the (6-4) TT lesion by Polη, and Polζ 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 Polη and Polζ, wherein Polη inserts a nucleotide opposite the 3′ T of the lesion and Polζ 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.

Original languageEnglish (US)
Pages (from-to)3558-3563
Number of pages6
JournalMolecular and cellular biology
Issue number10
StatePublished - 2001

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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