No abstract

Meiotic crossovers result from homology-directed repair of DNA double-strand breaks (DSBs). Unlike yeast and plants, where DSBs are generated near gene promoters, in many vertebrates DSBs are enriched at hotspots determined by the DNA binding activity of the rapidly evolving zinc finger array of PRDM9 (PR domain zinc finger protein 9). PRDM9 subsequently catalyzes tri-methylation of lysine 4 and lysine 36 of Histone H3 in nearby nucleosomes. Here, we identify the dual histone methylation reader ZCWPW1, which is tightly co-expressed during spermatogenesis with Prdm9, as an essential meiotic recombination factor required for efficient repair of PRDM9-dependent DSBs and for pairing of homologous chromosomes in male mice. In sum, our results indicate that the evolution of a dual histone methylation writer/reader (PRDM9/ZCWPW1) system in vertebrates remodeled genetic recombination hotspot selection from an ancestral static pattern near genes towards a flexible pattern controlled by the rapidly evolving DNA binding activity of PRDM9.

Edited by Ursula Jakob Two DNA methyltransferases, Dam and ␤-class cell cycleregulated DNA methyltransferase (CcrM), are key mediators of bacterial epigenetics. CcrM from the bacterium Caulobacter crescentus (CcrM C. crescentus, methylates adenine at 5-GANTC-3) displays 10 5-10 7-fold sequence discrimination against noncognate sequences. However, the underlying recognition mechanism is unclear. Here, CcrM C. crescentus activity was either improved or mildly attenuated with substrates having one to three mismatched bp within or adjacent to the recognition site, but only if the strand undergoing methylation is left unchanged. By comparison, single-mismatched substrates resulted in up to 10 6-fold losses of activity with ␣ (Dam) and ␥-class (M.HhaI) DNA methyltransferases. We found that CcrM C. crescentus has a greatly expanded DNA-interaction surface, covering six nucleotides on the 5 side and eight nucleotides on the 3 side of its recognition site. Such a large interface may contribute to the enzyme's high sequence fidelity. CcrM C. crescentus displayed the same sequence discrimination with singlestranded substrates, and a surprisingly large (>10 7-fold) discrimination against ssRNA was largely due to the presence of two or more riboses within the cognate (DNA) site but not outside the site. Results from C-terminal truncations and point mutants supported our hypothesis that the recently identified C-terminal, 80-residue segment is essential for dsDNA recognition but is not required for single-stranded substrates. CcrM orthologs from Agrobacterium tumefaciens and Brucella abortus share some of these newly discovered features of the C. crescentus enzyme, suggesting that the recognition mechanism is conserved. In summary, CcrM C. crescentus uses a previously unknown DNA recognition mechanism. The authors declare that they have no conflicts of interest with the contents of this article. This article contains Table S1 and Figs. S1-S8.

No abstract

Meiotic crossovers result from homology-directed repair of double strand breaks (DSBs). Unlike yeast and plants, where DSBs are generated near gene promoters, in many vertebrates, DSBs are enriched at hotspots determined by the DNA binding activity of the rapidly evolving zinc finger array of PRDM9 (PR domain zinc finger protein 9). PRDM9 subsequently catalyzes trimethylation of lysine 4 and lysine 36 of Histone H3 in nearby nucleosomes. Here, we identify the dual histone methylation reader ZCWPW1, which is tightly co-expressed during spermatogenesis with Prdm9 and co-evolved with Prdm9 in vertebrates, as an essential meiotic recombination factor required for efficient synapsis and repair of PRDM9-dependent DSBs. In sum, our results indicate that the evolution of a dual histone methylation writer/reader system in vertebrates facilitated a shift in genetic recombination away from a static pattern near genes towards a flexible pattern controlled by the rapidly evolving DNA binding activity of PRDM9.