Mismatch repair (MMR) proteins contribute to genome integrity by correcting replication errors. In higher eukaryotes, MMR proteins also regulate the cellular response to specific DNA damages caused by oxidization, alkylation or crosslinking. Previous studies have shown that MMR proteins were involved in the activation of apoptosis through p53-dependent and p53-independent mechanisms. MMR-deficient cells are known to be resistant to several DNA-damaging agents and exhibit variable defects in the induction of p53 and its related p73 proteins, which are activators of apoptosis. The mismatch repair protein PMS2 has been shown to bind with p73 and co-operate to induce apoptotic reaction to the DNA damages. On the other hand, the hetrodimer MLH1-PMS2 functions by making complex with MutS homologues which recognize replication errors or damaged legions on the genome. To examine whether MLH1 anticipate into the PMS2-p73 complex or not, we performed co-immunoprecipitation among PMS2, p73 and MLH1. Even though each MLH1-PMS2 complex and p73-PMS2 complex were co-precipitated, the ternary complex were not detected. To identify the binding site of PMS2 with p73, we then performed co-immunoprecipitation of full-length p73 with several fragments of PMS2 or full-length PMS2 with several fragments of p73. P73 interacted with PMS2 in the residue 500-700 which is a little N-terminal side from the binding site with MLH1. PMS2 interacted with p73 in the residue 1-322 most strongly but also with other site of p73 slightly, suggesting the interaction of p73 with PMS2 were mediated by several residues of p73. Our data indicating that the protein complexes MLH1-PMS2 and p73-PMS2 exist separately and MLH1 and p73 interact with the different sites of PMS2.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]