Figure 2.—

Comparison of the MutL and MutS homologs involved in the MMR spellchecker function (repair of errors introduced by DNA polymerase) and the MMR of mismatches formed during meiotic recombination. The relative contributions of each complex to the repair of base–base mismatches and four-base loop substrates are indicated by the arrow size. Msh2p/Msh6p/Mlh1p/Pms1p is involved in MMR of base–base mismatches in both contexts. Msh2p/Msh3p/Mlh1p/Pms1p initiates the majority of repair of four-base loops for the spellchecker function, with Msh2p/Msh3p/Mlh1p/Mlh2p and Msh2p/Msh3p/Mlh1p/Mlh3p making very small contributions (Wang et al. 1999; Harfe and Jinks-Robertson 2000). The meiotic repair of four-base loops is initiated primarily by Msh2p/Msh3p/Mlh1p/Pms1p, but an Mlh1-independent, Mlh3p-dependent complex (possibly Msh2p/Msh3p/Mlh3p/Mlh3p) is responsible for about one-third of the repair events.