Figure 6. Proposed mechanism of MMR action on intergenetional GAA repeat expansions.

Schematic images representing: (A) a small loop caused by triplex DNA structure; (B) recognition of the loop by the MutS complex, cleavage with endonuclease (ENDO), opening of the loop, recruitment of MutLα and synthesis of expanded DNA, and (C) end of repair by ligation of the further expanded strand and release of MMR proteins.