Mismatch repair-dependent iterative excision at irreparable O6-methylguanine lesions in human nuclear extracts.

Journal Article (Journal Article)

The response of mammalian cells to Sn1 DNA methylators depends on functional MutSalpha and MutLalpha. Cells deficient in either of these activities are resistant to the cytotoxic effects of this class of chemotherapeutic drug. Because killing by Sn1 methylators has been attributed to O6-methylguanine (MeG), we have constructed nicked circular heteroduplexes that contain a single MeG-T mispair, and we have examined processing of these molecules by mismatch repair in nuclear extracts of human cells. Excision provoked by MeG-T is restricted to the incised heteroduplex strand, leading to removal of the MeG when it resides on this strand. However, when the MeG is located on the continuous strand, the heteroduplex is irreparable. MeG-T-dependent repair DNA synthesis is observed on both reparable and irreparable 3' and 5' heteroduplexes as judged by [32P]dAMP incorporation. Labeling with [alpha-32P]dATP followed by a cold dATP chase has demonstrated that newly synthesized DNA on irreparable molecules is subject to re-excision in a reaction that is MutLalpha-dependent, an effect attributable to the presence of MeG on the template strand. Processing of the irreparable 3' heteroduplex is also associated with incision of the discontinuous strand of a few percent of molecules near the thymidylate of the MeG-T base pair. These results provide the first direct evidence for mismatch repair-mediated iterative processing of DNA methylator damage, an effect that may be relevant to damage signaling events triggered by this class of chemotherapeutic agent.

Full Text

Duke Authors

Cited Authors

  • York, SJ; Modrich, P

Published Date

  • August 11, 2006

Published In

Volume / Issue

  • 281 / 32

Start / End Page

  • 22674 - 22683

PubMed ID

  • 16772289

Pubmed Central ID

  • PMC2234603

International Standard Serial Number (ISSN)

  • 0021-9258

Digital Object Identifier (DOI)

  • 10.1074/jbc.M603667200


  • eng

Conference Location

  • United States