Antisense inhibition of the RAD51 enhances radiosensitivity

The mouse RecA-like gene Dmc1 is required for homologous chromosome synapsis during meiosis

The mouse Dmc1 gene is an E. coli RecA homolog that is specifically expressed in meiosis. The DMC1 protein was detected in leptotene-to-zygotene spermatocytes, when homolog pairing likely initiates. Targeted gene disruption in the male mouse showed an arrest of meiosis of germ cells at the early zygotene stage, followed by apoptosis. In female mice lacking the Dmc1 gene, normal differentiation of oogenesis was aborted in embryos, and germ cells disappeared in the adult ovary. Meiotic chromosome analysis of Dmc1-deficient mouse spermatocytes revealed random spread of univalent axial elements without correct pairing between homologs. In rare cases, however, we observed complex pairing among nonhomologs. Thus, the mouse Dmc1 gene is required for homologous synapsis of chromosomes in meiosis.

Mammalian Rad51 protein: a RecA homologue with pleiotropic functions

During the last years, homologues of E coli RecA have been cloned in numerous species including man. These Rad51 proteins share sequence as well as functional homologies with the bacterial protein. Human Rad51 (HsRad51) is able to catalyze strand exchange in vitro between homologous DNAs, but with a lower efficiency compared to that of RecA. This suggests the requirement of additional factors. A very interesting feature of Rad51 is its essential role in mouse which could mean that it has gained an essential function in cell growth. The interaction of HsRad51 with several tumor suppressor genes namely p53, BRCA1 and BRCA2 implies possible role(s) of this protein in tumorigenesis. Thus, the continued study of Rad51 should bring important insights not only into homologous recombination mechanisms but also into cell proliferation regulation.

The Drosophila melanogaster RAD54 homolog, DmRAD54, is involved in the repair of radiation damage and recombination

The RAD54 gene of Saccharomyces cerevisiae plays a crucial role in recombinational repair of double-strand breaks in DNA. Here the isolation and functional characterization of the RAD54 homolog of the fruit fly Drosophila melanogaster, DmRAD54, are described. The putative Dmrad54 protein displays 46 to 57% identity to its homologs from yeast and mammals. DmRAD54 RNA was detected at all stages of fly development, but an increased level was observed in early embryos and ovarian tissue. To determine the function of DmRAD54, a null mutant was isolated by random mutagenesis. DmRADS4-deficient flies develop normally, but the females are sterile. Early development appears normal, but the eggs do not hatch, indicating an essential role for DmRAD54 in development. The larvae of mutant flies are highly sensitive to X rays and methyl methanesulfonate. Moreover, this mutant is defective in X-ray-induced mitotic recombination as measured by a somatic mutation and recombination test. These phenotypes are consistent with a defect in the repair of double-strand breaks and imply that the RAD54 gene is crucial in repair and recombination in a multicellular organism. The results also indicate that the recombinational repair pathway is functionally conserved in evolution.