The Saccharomyces cerevisiae Mlh1-Mlh3 heterodimer is an endonuclease that preferentially binds to Holliday junctions.

ABSTRACT: MutL?, a heterodimer of the MutL homologues Mlh1 and Mlh3, plays a critical role during meiotic homologous recombination. The meiotic function of Mlh3 is fully dependent on the integrity of a putative nuclease motif DQHAX2EX4E, inferring that the anticipated nuclease activity of Mlh1-Mlh3 is involved in the processing of joint molecules to generate crossover recombination products. Although a vast body of genetic and cell biological data regarding Mlh1-Mlh3 is available, mechanistic insights into its function have been lacking due to the unavailability of the recombinant protein complex. Here we expressed the yeast Mlh1-Mlh3 heterodimer and purified it into near homogeneity. We show that recombinant MutL? is a nuclease that nicks double-stranded DNA. We demonstrate that MutL? binds DNA with a high affinity and shows a marked preference for Holliday junctions. We also expressed the human MLH1-MLH3 complex and show that preferential binding to Holliday junctions is a conserved capacity of eukaryotic MutL? complexes. Specific DNA recognition has never been observed with any other eukaryotic MutL homologue. MutL? thus represents a new paradigm for the function of the eukaryotic MutL protein family. We provide insights into the mode of Holliday junction recognition and show that Mlh1-Mlh3 prefers to bind the open unstacked Holliday junction form. This further supports the model where MutL? is part of a complex acting on joint molecules to generate crossovers in meiosis.

SUBMITTER: Ranjha L 

PROVIDER: S-EPMC3937642 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature