Fig. 3.

Model for Exo1-independent mismatch repair. Results presented here are consistent with the 2-stage mechanism shown. MutLα endonuclease, which is activated on a nicked DNA in a mismatch-, MutSα-, RFC, and PCNA-dependent manner, introduces additional breaks into the incised DNA strand in a manner biased to the distal side of the mispair (10). The multiply-nicked product serves as substrate for DNA polymerase δ, which is capable of synthesis-driven strand displacement (20), resulting in coordinate displacement of a DNA segment spanning the mismatch and heteroduplex repair.