Changes in chromatin structure at recombination initiation sites during yeast meiosis.

Abstract

Transient double‐strand breaks (DSBs) occur during Saccharomyces cerevisiae meiosis at recombination hot spots and are thought to initiate most, if not all, homologous recombination between chromosomes. To uncover the regulatory mechanisms active in DSB formation, we have monitored the change in local chromatin structure at the ARG4 and CYS3 recombination hot spots over the course of meiosis. Micrococcal nuclease (MNase) digestion of isolated meiotic chromatin followed by indirect end‐labeling revealed that the DSB sites in both loci are hypersensitive to MNase and that their sensitivity increases 2‐ to 4‐fold prior to the appearance of meiotic DSBs and recombination products. Other sensitive sites are not significantly altered. The study of hyper‐ and hypo‐recombinogenic constructs at the ARG4 locus, also revealed that the MNase sensitivity at the DSB site correlates with both the extent of DSBs and the rate of gene conversion. These results suggest that the local chromatin structure and its modification in early meiosis play an important role in the positioning and frequency of meiotic DSBs, leading to meiotic recombination.

Sensing of DNA non‐homology lowers the initiation of meiotic recomination in yeast

“…Factors other than primary DNA sequence, most notably chromatin structure, are likely to be involved in the control of the amount and position of DSBs. In several chromosomal regions, DSBs were found to co-localize with DNase I and MNase hypersensitive sites (Wu & Lichten 1994;Ohta et al 1994), and changes in chromatin structure were found to correlate with the formation of DSBs (Ohta et al 1994). Additional studies have shown that the recombinational hot-spot activity is also controlled by transacting factors.…”

“…It has been shown that MNase hypersensitivity increases early in meiosis, before DSB formation (Ohta et al 1994). A way to incorporate this change in chromatin, interstitial pairing (Weiner & Kleckner 1994) and DSB formation during meiosis would be to assume that the modification of chromatin structures early in meiosis that occurs in nucleosome-free regions is a consequence of the processes of interhomologue crosstalk signalling the presence of DNA identity.…”

The histone methylase Set2p and the histone deacetylase Rpd3p repress meiotic recombination at the HIS4 meiotic recombination hotspot in Saccharomyces cerevisiae

“…There are several lines of evidence that the frequency of DSBs is regulated by elements of chromatin structure rather than primary DNA sequence (2). First, recombination hotspots exhibit hypersensitivity to nucleases (6)(7)(8)(9)(10). Some loci (8,9) undergo meiosis-specific alterations in nuclease sensitivity prior to DSB formation, although no such changes are observed at other loci (6).…”

“…First, recombination hotspots exhibit hypersensitivity to nucleases (6)(7)(8)(9)(10). Some loci (8,9) undergo meiosis-specific alterations in nuclease sensitivity prior to DSB formation, although no such changes are observed at other loci (6). Since all nuclease-hypersensitive regions are not meiotic recombination hotspots (6,10), "open" chromatin appears necessary, but not sufficient, for meiotic recombination hotspot activity.…”

Communication between homologous chromosomes: genetic alterations at a nuclease‐hypersensitive site can alter mitotic chromatin structure at that site both in cis and in trans

“…Second, meiotic recombination in yeast is mediated largely or exclusively by meiosis-specific double strand breaks (DSBs), and these breaks occur in a sequence nonspecific manner in regions of chromatin that are accessible, i.e. regions that are especially sensitive to nuclease digestion in both meiotic and mitotic cells (Wu & Lichten 1994;Ohta et al 1994). Thus, if pairing interactions also occurred in such regions, it would be possible to envision that mitotic and meiotic chromosome pairing and meiotic recombination represent a single sequential series of events occurring in nucleosome-free regions, with increasingly stable interactions between intact chromosomes preceding and culminating in the occurrence of DSBs (Kleckner & Weiner 1993;Weiner & Kleckner 1994).…”