Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.
Nat Struct Mol Biol. 2010 Mar;17(3):379-88. doi: 10.1038/nsmb.1771. Epub 2010 Feb 14.
The aromatic amine carcinogen 2-aminofluorene (AF) forms covalent adducts with DNA, predominantly with guanine at the C8 position. Such lesions are bypassed by Y-family polymerases such as Dpo4 via error-free and error-prone mechanisms. We show that Dpo4 catalyzes elongation from a correct 3'-terminal cytosine opposite [AF]G in a nonrepetitive template sequence with low efficiency. This extension leads to cognate full-length product, as well as mis-elongated products containing base mutations and deletions. Crystal structures of the Dpo4 ternary complex, with the 3'-terminal primer cytosine base opposite [AF]G in the anti conformation and with the AF moiety positioned in the major groove, reveal both accurate and misalignment-mediated mutagenic extension pathways. The mutagenic template-primer-dNTP arrangement is promoted by interactions between the polymerase and the bulky lesion rather than by a base pair-stabilized misaligment. Further extension leads to semitargeted mutations via this proposed polymerase-guided mechanism.
芳香胺类致癌物质 2-氨基芴（AF）与 DNA 形成共价加合物，主要是在 C8 位置与鸟嘌呤结合。这种损伤可以通过 Y 家族聚合酶（如 Dpo4）通过无错和易错机制绕过。我们表明，Dpo4 通过无错和易错机制，以低效率催化从正确的 3'末端胞嘧啶与非重复模板序列中 [AF]G 的延伸。这种延伸导致同源全长产物，以及含有碱基突变和缺失的误延伸产物。Dpo4 三元复合物的晶体结构，其中 3'末端引物胞嘧啶碱基与反式构象中的 [AF]G 相对，并且 AF 部分位于大沟中，揭示了准确和错配介导的诱变延伸途径。聚合酶与大体积损伤之间的相互作用而不是碱基配对稳定的错配促进了诱变模板-引物-dNTP 排列。通过这种提议的聚合酶指导机制，进一步延伸会导致半靶向突变。
