同源重组是发生在雌雄配子减数分裂过程中的重要事件，在这一过程中，来自父本和母本的同源染色体之间发生遗传物质的交换，并稳定遗传给下一代。近期研究认为，哺乳动物细胞的同源重组与一种叫做PRDM9（PR domain containing 9）的组蛋白H3甲基转移酶的活性有关。研究人员认为PRDM9能够通过其高度重复的锌指结构域结合特定DNA序列，从而使结合该蛋白多的区域成为同源重组热点区域。本文中，研究者发现敲除了PRDM9基因的小鼠仍然可以发生同源重组。
研究者对缺失了PRDM9基因的小鼠、有不同prdm9等位基因的2个小鼠品系，以及它们杂交的子代进行了比较，发现PRDM9确实是决定除了假常染色体以为基因组所有区域重组热点的关键基因。令人惊讶的是，PRDM9敲除的小鼠不但能够进行同源重组，而且与野生型小鼠相同，在这些重组的热点区域也能够检测到组蛋白H3K4甲基化的标志。但是，在缺失了PRDM9基因的小鼠细胞中，同源重组大多发生在启动子区，以及一些不依赖PRDM9的H3K4甲基化区域。而这些区域在野生型小鼠的细胞中很少发生同源重组。这一结果可能说明，PRDM9在同源重组中起到区分基因组中不同功能元件的作用。（生物谷 Bioon.com ）
doi:10.1038/nature11089
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Genetic recombination is directed away from functional genomic elements in mice
Kevin Brick, Fatima Smagulova, Pavel Khil, R. Daniel Camerini-Otero & Galina V. Petukhova
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, 2, 3, 4, 5, 6, the product of the only known speciation-associated gene in mammals7. PRDM9 is thought to determine the preferred recombination sites—recombination hotspots—through sequence-specific binding of its highly polymorphic multi-Zn-finger domain8. Nevertheless, Prdm9 knockout mice are proficient at initiating recombination9. 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 F1 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 cells10. 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.
