http://repub.eur.nl/res/aut/15987/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/29698/ 2008-12-15T00:00:00Z The sensitivity of DNA-repair-deficient Rad54/Rad54B mice for clastogens was studied and compared to that of wild-type mice. LacZ mutant frequencies (MF) in Rad54/Rad54B mice, after treatment with mitomycin C (MMC), bleomycin (BLM) and γ-irradiation, were compared to those of the wild-type mice following the same treatments. While none of the clastogens showed an induction of the lacZ MF in the wild-type mice, there was a significant increase of the lacZ MF in the bone marrow of the Rad54/Rad54B mice after treatment with BLM and γ-irradiation and in the spleen after MMC treatment. As expected, the positive control ENU showed a significant increase in the lacZ MF in all tested organs in wild-type mice. Mutant colonies were hybridized with total mouse DNA in order to discriminate between small gene mutations and large DNA rearrangements and translocations (size-change mutations). The hybridization studies showed a significant increase in mouse DNA positive clones 4 days after treatment with MMC and BLM in the bone marrow of the wild-type mice, which is indicative for chromosomal rearrangements and translocations to occur. An even more pronounced increase was seen 28 days after treatment with the same compounds in the Rad54/Rad54B mice. http://repub.eur.nl/res/pub/13976/ 2006-02-01T00:00:00Z Homologous recombination is a versatile DNA damage repair pathway requiring Rad51 and Rad54. Here we show that a mammalian Rad54 paralog, Rad54B, displays physical and functional interactions with Rad51 and DNA that are similar to those of Rad54. While ablation of Rad54 in mouse embryonic stem (ES) cells leads to a mild reduction in homologous recombination efficiency, the absence of Rad54B has little effect. However, the absence of both Rad54 and Rad54B dramatically reduces homologous recombination efficiency. Furthermore, we show that Rad54B protects ES cells from ionizing radiation and the interstrand DNA cross-linking agent mitomycin C. Interestingly, at the ES cell level the paralogs do not display an additive or synergic interaction with respect to mitomycin C sensitivity, yet animals lacking both Rad54 and Rad54B are dramatically sensitized to mitomycin C compared to either single mutant. This suggests that the paralogs possibly function in a tissue-specific manner. Finally, we show that Rad54, but not Rad54B, is needed for a normal distribution of Rad51 on meiotic chromosomes. Thus, even though the paralogs have similar biochemical properties, genetic analysis in mice uncovered their nonoverlapping roles.