FIG 1.

Schematic diagram of the mismatch repair (MMR) pathway that rectifies errors arising from DNA replication in Saccharomyces cerevisiae. Mismatches are recognized by the Msh heterodimers. The Msh2-Msh6 heterodimer primarily identifies base-base and single insertion/deletion (1-bp) mismatches, the Msh2-Msh3 heterodimer primarily identifies longer insertion/deletion loop (≥2-bp) mismatches, and the Mlh1-Pms1 heterodimer directs downstream events. Replication factor C (RFC) loads the proliferating cell nuclear antigen (PCNA), which interacts with various proteins and is involved in multiple steps in the pathway (although it is shown once for simplicity). Lesions in the newly synthesized strand are then excised by exonuclease 1 (Exo1), while the replication protein A (RPA) binds to single-stranded DNA (ssDNA). The DNA polymerase, Pol δ, synthesizes the new strand, and ligase I ligates the fragments of the new strand.