Table 1.

Identity and functions of E. coli and eukaryotic proteins involved in MMR of replication errors

E. coli protein	Function	Homologues	Function
MutS	Binds mismatches	MSH2-MSH6 (MutSα)	Repairs single base-base and 1 –2 base IDL mismatches
		MSH2-MSH3 (MutSβ)	Repair of some single base IDLs and IDLs ≥2 bases Partially redundant with Msh2-Msh6
MutL	Matchmaker that coordinates multiple steps in MMR	MLH1-PMS2 (yPMS1) (MutLα) MLH1-MLH2 (hPMS1) (MutLβ) MLH1-MLH3 (MutLγ)	Matchmaker for coordinating events from mismatch binding by MutS homologues to DNA repair synthesis Endonuclease (PMS2) Function of human heterodimer unknown Suppresses some IDL mutagenesis in yeast Suppresses some IDL mutagenesis Participates in meiosis
MutH	Nicks nascent unmethylated strand at hemimethylated CATC sites	None
γ-δ complex	Loads β-clamp onto DNA	RFC complex	Loads PCNA, modulates excision polarity
β-Clamp	Interacts with MutS and may recruit it to mismatches and/or the replication fork	PCNA	Interacts with MutS and MutL homologues
	Enhances processivity of DNA pol III		Recruits MMR proteins to mismatches Increases MM binding specificity of Msh2–Msh6 Participates in excision and probably in signalling Participates in DNA repair synthesis Participates in DNA re-synthesis
Helicase II	Loaded onto DNA at nick by MutS and MutL	None
	Unwinds DNA to allow excision of ssDNA
ExoI, ExoX	Perform 3′ –5′ excision of ssDNA	EXOI(Rth1)	Excision of dsDNA
RecJ	Perform 5′ –3′ excision of ssDNA (also 3′-5′ excision by ExoVII)	3′ exo of polδ	Excision of ssDNA
ExoVII		3′ exo of polε	Synergistic mutator with Exo1 mutant
DNA pol III	Accurate re-synthesis of DNA	DNA polδ	Accurate repair synthesis
SSB	Participates in excision and DNA synthesis	RPA	Participates in excision and in DNA synthesis
DNA ligase	Seals nicks after completion of DNA synthesis	DNA ligase	Seals nicks after completion of DNA synthesis

Adapted from Kunkel and Erie (2005) with permission.