In Saccharomyces cerevisiae, the Hop2 protein forms a complex with the Mnd1 protein and is required for the alignment of homologous chromosomes during meiosis, probably through extensive homology matching between them. The Rad51 and Dmc1 proteins, the eukaryotic RecA orthologs, promote strand exchange and may function in the extensive matching of homology within paired DNA molecules. In the present study, we purified the human TBPIP/Hop2-Mnd1 complex and found that it significantly stimulates the Dmc1- and Rad51-mediated strand exchange. The human Hop2-Mnd1 complex preferentially binds to a three-stranded DNA branch, which mimics the strand-exchange intermediate. These findings are consistent with genetic data, which showed that the Hop2 and Mnd1 proteins are required for homology matching between homologous chromosomes. Therefore, the human TBPIP/Hop2-Mnd1 complex may ensure proper pairing between homologous chromosomes through its stimulation of strand exchange during meiosis.
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