Figure 3.

The exonuclease function is required for Exo1-dependent mismatch repair in mouse cell extract. Mismatch repair was scored using G-T heteroduplex DNA containing a 5′- (panel A) or 3′- (panel B) strand break in whole cell extract prepared from Mlh1^−/−Exo1^−/− MEF cells. Extracts were supplemented with MutLα as indicated and assays performed in the absence (dilution buffer only) or presence of Exo1-D173A, Exo1-E109K or wild type Exo1 (Materials and Methods). Mismatch repair, which converts the heteroduplex to a HindIII-sensitive form, was determined after cleavage with HindIII and ClaI.