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Genetic recombination occurs during meiosis, the key developmental programme of gametogenesis. Recombination in mammals has been recently linked to the activity of a histone H3 methyltransferase, PR domain containing 9 (PRDM9) (1-6), the product of the only known speciation-associated gene in mammals (7). PRDM9 is thought to determine the preferred recombination sites--recombination hotspots--through sequence-specific binding of its highly polymorphic multi-Zn-finger domain (8). Nevertheless, Prdm9 knockout mice are proficient at initiating recombination (9). Here we map and analyse the genome-wide distribution of recombination initiation sites in Prdm9 knockout mice and in two mouse strains with different Prdm9 alleles and their [F.sub.1] hybrid. We show that PRDM9 determines the positions of practically all hotspots in the mouse genome, with the exception of the pseudo-autosomal region (PAR)--the only area of the genome that undergoes recombination in 100% of cells (10). Surprisingly, hotspots are still observed in Prdm9 knockout mice, and as in wild type, these hotspots are found at H3 lysine 4 (H3K4) trimethylation marks. However, in the absence of PRDM9, most recombination is initiated at promoters and at other sites of PRDM9-independent H3K4 trimethylation. Such sites are rarely targeted in wild-type mice, indicating an unexpected role of the PRDM9 protein in sequestering the recombination machinery away from gene-promoter regions and other functional genomic elements., Homologous recombination is initiated by the introduction of DNA double-stranded breaks (DSBs) by the SPO11 protein (11), and we have previously shown that recombination sites can be mapped by sequencing [...]

Hot spots for meiotic recombination To initiate the recombination process that guides accurate chromosome segregation during meiosis, programmed double-strand breaks are made at preferred sites known as hot spots. Petukhova and colleagues have now achieved high-resolution genome-wide mapping of meiotic double-strand breaks in mouse cells. The method employed is independent of the availability of genetic markers, a limitation of previous approaches. With these data they have uncovered several features of hot spots at both the sequence and chromatin levels. Meiotic recombination predominantly occurs at discrete genomic loci called recombination hotspots, but the features defining these areas are still largely unknown (reviewed in refs 1-5). To allow a comprehensive analysis of hotspot-associated DNA and chromatin characteristics, we developed a direct molecular approach for mapping meiotic DNA double-strand breaks that initiate recombination. Here we present the genome-wide distribution of recombination initiation sites in the mouse genome. Hotspot centres are mapped with approximately 200-nucleotide precision, which allows analysis of the fine structural details of the preferred recombination sites. We determine that hotspots share a centrally distributed consensus motif, possess a nucleotide skew that changes polarity at the centres of hotspots and have an intrinsic preference to be occupied by a nucleosome. Furthermore, we find that the vast majority of recombination initiation sites in mouse males are associated with testis-specific trimethylation of lysine 4 on histone H3 that is distinct from histone H3 lysine 4 trimethylation marks associated with transcription. The recombination map presented here has been derived from a homogeneous mouse population with a defined genetic background and therefore lends itself to extensive future experimental exploration. We note that the mapping technique developed here does not depend on the availability of genetic markers and hence can be easily adapted to other species with complex genomes. Our findings uncover several fundamental features of mammalian recombination hotspots and underline the power of the new recombination map for future studies of genetic recombination, genome stability and evolution., Author(s): Fatima Smagulova [sup.1] , Ivan V. Gregoretti [sup.2] , Kevin Brick [sup.2] , Pavel Khil [sup.2] , R. Daniel Camerini-Otero [sup.2] , Galina V. Petukhova [sup.1] Author Affiliations: (1) [...]

The recombinase activity of Rad51 is stimulated by a bipartite complex formed by genes Hop2-Mnd1. The Hop2 acts as the major DNA binding subunit while Mnd1 is the Rad51 interaction entity.