MutLα interacts with Microprocessor and pri-miR-422a. (A) Purified recombinant proteins used in this study. (B, C) Effect of MutLα on pri-miR-422a interactions with DGCR8 (B) and Drosha (C). (D) Binding of pri-miR-422a by wild-type (WT) and mutant MutLα proteins. (E, F) Co-immunoprecipitation (Co-IP) of MLH1 and Microprocessor in HeLa whole-cell extracts (E) and purified proteins (F). Co-IP reactions were performed using an MLH1 antibody and individual proteins were detected using their corresponding antibodies, as indicated. NMS, non-immune mouse serum; HC, IgG heavy chain.