The protein MutL is essential in mismatch repair as it coordinating multiple protein-protein interactions that signal strand removal upon mismatch recognition by MutS. MutL is composed of two structurally conserved domains connected by a variable flexible linker: an N-terminal ATPase domain and C-terminal dimerisation domain PMID:15470502. The latter harbours the the endonuclease activity of the protein. Structural studies have shown that this C-terminal region is organized into a dimerization and a regulatory subdomain connected by a helical lever spanning the conserved endonuclease motif. Structural domains comprising this superfamily share the structure of the regulatory subdomain of the C-terminal domain of the MutL protein PMID:20603082.