The interaction of DNA mismatch repair proteins with human exonuclease I

Exonucleolytic degradation of DNA is an essential part of many DNA metaboli c processes including DNA mismatch repair (MMR) and recombination. Human ex onuclease I (hExoI) is a member of a family of conserved 5' --> 3' exonucle ases, which are implicated in these processes by genetic studies. Here, we demonstrate that hExoI binds strongly to hMLH1, and we describe interaction regions between hExoI and the MMR proteins hMSH2, hMSH3, and hMLH1. In add ition, hExoI forms an immunoprecipitable complex with hMLH1/hPMS2 in vivo. The study of interaction regions suggests a biochemical mechanism of the in volvement of hExoI as a downstream effector in MMR and/or DNA recombination .