2010/03/05

Bypass of an aromatic amine lesion by Y-family polymerase Dpo4.

An international team of researchers from MSKCC (USA), NYU (USA) and CICbioGUNE reported a detailed insight into the mechanisms by which Dpo4, a member of the Y-family DNA polymerases, bypasses an aromatic amine lesion. To do this, researchers solved crystal structures of the polymerase at different stages of replication past an [AF]G-modified DNA template. These structures act as snapshots of this polymerase as it progresses through extension of a primer strand with a correct C base as well as an incorrect A-base opposite the [AF]G lesion in a template strand. Unexpectedly, these structures reveal that the extension from a correct C base can occur in both error-free and error-prone manner. In the former case, the bases of the primer strand are properly aligned with the damaged template strand. In contrast, in the latter case, the primer-template DNA past the damaged site is misaligned, while a partner C base paired correctly with the damaged G. Surprisingly, favorable interactions of the bulky AF carcinogen with the polymerase appear to be a driving force for a formation of such misaligned mutagenic structure. The followed up biochemical studies confirmed that Dpo4 polymerases forms both, correct and incorrect, primer DNA products during extension from a correct C positioned opposite the AF-damaged G. Thus, based on these findings the authors propose a novel polymerase-stabilized mechanism for generating semi-targeted mutations.

Reference:
Rechkoblit O, Kolbanovskiy A, Malinina L, Geacintov NE, Broyde S, Patel DJ. (2010) Mechanism of error-free and semitargeted mutagenic bypass of an aromatic amine lesion by Y-family polymerase Dpo4. Nat Struct Mol Biol. 2010 Feb 14. [Epub ahead of print]