Functional studies on the candidate ATPase domains of Saccharomyces cerevisiae MutLα

Saccharomyces cerevisiae MutL homologues Mlh1p and Pms1p form a heterodimer, termed MutL alpha, that is required for DNA mismatch repair after mismatch binding by MutS homologues. Recent sequence and structural studies have placed the NH2 termini of MutL homologues in a new family of ATPases. To address the functional significance of this putative ATPase activity in MutL alpha, we mutated conserved motifs for ATP hydrolysis and ATP binding in both Mlh1p and Pms1p and found that these changes disrupted DNA mismatch repair in vivo. Limited proteolysis with purified recombinant MutL alpha demonstrated that the NH2 terminus of MutL alpha undergoes conformational changes in the presence of ATP and nonhydrolyzable ATP analogs. Furthermore, two-hybrid analysis suggested that these ATP-binding-induced conformational changes promote an interaction between the NH2 termini of Mlh1p and Pms1p. Surprisingly, analysis of specific mutants suggested differential requirements for the ATPase motifs of Mlh1p and Pms1p during DNA mismatch repair. Taken together, these results suggest that MutL alpha undergoes ATP-dependent conformational changes that may serve to coordinate downstream events during yeast DNA mismatch repair.