Human exonuclease I is required for 5' and 3' mismatch repair.

Journal Article (Journal Article)

We have partially purified a human activity that restores mismatch-dependent, bi-directional excision to a human nuclear extract fraction depleted for one or more mismatch repair excision activities. Human EXOI co-purifies with the excision activity, and the purified activity can be replaced by near homogeneous recombinant hEXOI. Despite the reported 5' to 3' hydrolytic polarity of this activity, hEXOI participates in mismatch-provoked excision directed by a strand break located either 5' or 3' to the mispair. When the strand break that directs repair is located 3' to the mispair, hEXOI- and mismatch-dependent gap formation in excision-depleted extracts requires both hMutSalpha and hMutLalpha. However, excision directed by a 5' strand break requires hMutSalpha but can occur in absence of hMutLalpha. In systems comprised of pure components, the 5' to 3' hydrolytic activity of hEXOI is activated by hMutSalpha in a mismatch-dependent manner. These observations indicate a hydrolytic function for hEXOI in 5'-heteroduplex correction. The involvement of hEXOI in 3'-heteroduplex repair suggests that it has a regulatory/structural role in assembly of the 3'-excision complex or that the protein possesses a cryptic 3' to 5' hydrolytic activity.

Full Text

Duke Authors

Cited Authors

  • Genschel, J; Bazemore, LR; Modrich, P

Published Date

  • April 12, 2002

Published In

Volume / Issue

  • 277 / 15

Start / End Page

  • 13302 - 13311

PubMed ID

  • 11809771

International Standard Serial Number (ISSN)

  • 0021-9258

Digital Object Identifier (DOI)

  • 10.1074/jbc.M111854200


  • eng

Conference Location

  • United States