The Saccharomyces cerevisiae Mlh1-Mlh3 Heterodimer Is an Endonuclease That Preferentially Binds to Holliday Junctions
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Authors: | Lepakshi Ranjha Roopesh Anand Petr Cejka |
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Institution: | From the Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland |
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Abstract: | MutLγ, 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 MutLγ is a nuclease that nicks double-stranded DNA. We demonstrate that MutLγ 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 MutLγ complexes. Specific DNA recognition has never been observed with any other eukaryotic MutL homologue. MutLγ 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 MutLγ is part of a complex acting on joint molecules to generate crossovers in meiosis. |
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Keywords: | DNA-binding Protein DNA Mismatch Repair DNA Repair Homologous Recombination Meiosis DNA Endonuclease Holliday Junction Mlh1 Mlh3 MutLγ |
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