Fig. 1.

Exo1-independent 3′ directed mismatch repair extracts of MEFs. Mismatch repair and mismatch-provoked excision in extracts of Mlh1^−/− Exo1^−/− MEF cells were determined as described in Materials and Methods. Reactions were supplemented with MutLα and Exo1 as indicated or with MutLαD699N, which contains an amino acid substitution in the PMS2 metal binding motif that renders the MutLα endonuclease nonfunctional (10). (A) Mismatch repair, which restores a HindIII site, was scored by cleavage with HindIII and ClaI. (B) Mismatch-provoked excision under conditions of repair DNA synthesis block was scored by cleavage with NheI and ClaI. Excision renders the NheI site 5 bp from the mismatch resistant to hydrolysis. (C) 3′ and 5′ Directed mismatch repair and mismatch-provoked excision in MEF cell extracts. Results shown are the average of 4 independent experiments like those in A and B and Fig. S1. Excision values are corrected for 0 time background. Error bars correspond to 1 SD.