The meiosis-specific recombinase hDmc1 forms ring structures and interactswith hRad51

Eukaryotic cells encode two homologs of Escherichia coli RecA protein, Rad5 1 and Dmc1, which are required for meiotic recombination. Rad51, like E.col i RecA, forms helical nucleoprotein filaments that promote joint molecule a nd heteroduplex DNA formation. Electron microscopy reveals that the human m eiosis-specific recombinase Dmc1 forms ring structures that bind single-str anded (ss) and double-stranded (ds) DNA, The protein binds preferentially t o ssDNA tails and gaps in duplex DNA. hDmc1-ssDNA complexes exhibit an irre gular, often compacted structure, and promote strand-transfer reactions wit h homologous duplex DNA, hDmc1 binds duplex DNA with reduced affinity to fo rm nucleoprotein complexes. In contrast to helical RecA/Rad51 filaments, ho wever, Dmc1 filaments are composed of a linear array of stacked protein rin gs. Consistent with the requirement for two recombinases in meiotic recombi nation, hDmc1 interacts directly with hRad51.