Biochemical characterization of Dmc1, a meiosis-specific recombinase

The repair of double strand breaks (DSBs) created in meiosis ensures proper segregation of homologous chromosomes during the first meiotic division. Dmc1 and Rad51 are eukaryotic RecA homologues that are involved in the repair of these breaks by homologous recombination. The expression of Dmc1 is limited to meiosis while Rad51 is expressed in mitosis and meiosis. Dmc1 and Rad51 have unique and overlapping functions during meiotic recombination. Purification of the Dmc1 protein from the budding yeast Saccharomyces cerevisiae and basic characterization of its biochemical activity are presented in this study. The protein has a weak DNA-dependent ATPase activity and binds both single-strand DNA (ssDNA) and double-strand DNA (dsDNA). Electrophoretic mobility shift assays suggest that DNA binding by ScDmc1 is cooperative. ScDmc1 renatures linearized plasmid DNA with first order reaction kinetics and without requiring added nucleotide cofactor. In addition, ScDmc1 catalyzes strand assimilation of ssDNA oligonucleotides into homologous supercoiled duplex DNA in a reaction promoted by ATP or the non-hydrolyzable ATP analog AMP-PNP.; The repair of DSBs is facilitated by multiple accessory factors. Rad54 and Tid1 are members of the SWI/SNF family that work with the RecA homologues to repair meiotic DSBs. The strand assimilation activity of Rad51 is stimulated in the presence of Rad54 and Tid1. This study shows that the strand assimilation activity of ScDmc1 is also stimulated by Rad54 and Tid1. Rad54 and Tid1 increase the level of products formed by strand assimilation. Optimal stimulation of ScDmc1 strand assimilation activity requires the ATPase activity of Tid1. Tid1 extends the range of ssDNA substrates that are suitable for ScDmc1 strand assimilation activity.; The data provide additional evidence that Dmc1 is a functional RecA homologue and provides biochemical evidence for the role of Tid1 in stimulating Dmc1 activity. How these results contribute to understanding the mechanism of strand assimilation and the coordination of the RecA homologues during meiosis are discussed.