prophase I arrest in males and sister chromatid separation at metaphase II in females

Bacterial RecA and its yeast orthologue RAD51 are the founding members of the RecA/RAD51 protein family, which plays a crucial role in DNA repair by homologous recombination (for review see Kawabata et al., 2005). After DNA ends are resected at the site of a DNA break, these proteins form a nucleoprotein fi lament on the single-stranded DNA and catalyze a strand invasion and strand exchange reaction with a homologous region on another DNA molecule to ensure faithful DNA repair. In addition to RAD51, a few other RAD51-like proteins were found in eukaryotes, with their number increasing from three in budding yeast (Rad55, Rad57, and Dmc1) to six in most of the higher eukaryotes (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3, and DMC1; Dosanjh et al., 1998). These proteins have 20–30% amino acid sequence similarity and share common functional domains (Miller et al., 2004). The core C-terminal domain contains two functionally important ATP-binding Walker A and B motifs and is linked to a small globular N-terminal domain via a linker region that is important for protein–protein interactions. Except for DMC1, a meiosis-specifi c protein with functions overlapping those of RAD51 (Bishop et al., 1992), the other fi ve paralogues are auxiliary to RAD51. In yeast, the purifi ed Rad55/Rad57 heterodimer functions as a mediator of Rad51, enabling it to nucleate on single-stranded DNA in the presence of replication protein A (RPA; Sung, 1997). Chicken DT40 RAD51C defi ciency in mice results in early prophase I arrest in males and sister chromatid separation at metaphase II in females