Position- and orientation-independent activity of the Schizosaccharomyces pombe meiotic recombination hot spot  M26

Abstract

The activity of the M26 meiotic recombination hot spot of Schizosaccharomyces pombe depends on the presence of the heptamer 5-ATGACGT-3. Transplacement of DNA fragments containing the ade6-M26 gene to other chromosomal loci has previously demonstrated that the heptamer functions in some, but not all, transplacements, suggesting that hot spot activity depends on chromosomal context. In this study, hot spot activity was tested in the absence of gross DNA changes by using site-directed mutagenesis to create the heptamer sequence at novel locations in the genome. When created by mutagenesis of 1-4 bp in the ade6 and ura4 genes, the heptamer was active as a recombination hot spot, in an orientation-independent manner, at all locations tested. Thus, the heptamer sequence can create an active hot spot in other chromosomal contexts, provided that the gross chromosomal structure is not altered; this result is consistent with the hypothesis that a specific higher-order chromatin structure is required for M26 hot spot activity.Homologous recombination, the exchange of genetic information between homologous DNA duplexes, plays a vital role in the generation of genetic diversity, in the proper segregation of chromosomes during meiosis, and in the repair of DNA damage in somatic cells. Although homologous recombination occurs throughout the genome, some sites, termed hot spots, exhibit elevated frequencies of exchange. Recombination hot spots have been described in diverse organisms from bacteria to mammals (1, 2). Because hot spots appear to enhance a rate-limiting step of recombination, determination of the molecular mechanism by which hot spots act will increase our understanding of an important stage of homologous recombination.The M26 mutation of the fission yeast Schizosaccharomyces pombe creates a meiotic recombination hot spot in the ade6 gene. M26 is one of 394 mutations in ade6 described by Gutz (3) and results from a G 3 T transversion in the coding region of the ade6 gene (4, 5). Among these 394 mutations, M26 is unique; in heteroallelic crosses, it recombines with other ade6 mutations up to 15-fold more frequently than the adjacent M375 mutation does (3). M375 is an equivalent G 3 T transversion in the preceding codon and thus serves as an ideal genetic control for M26 (4). M26 undergoes gene conversion 10 times more frequently than M375 and demonstrates disparity of conversion, with preferential conversion of M26 to wild type, whereas M375 converts with near parity (3). M26 also increases the frequency of conversion of other ade6 mutations, with which it frequently coconverts; the frequency of coconversion decreases with increasing distance from M26 (6). These properties led Gutz (3) to propose that the M26 mutation creates a site that stimulates recombination near itself and, less frequently, at a distance.M26 is unique among eukaryotic hot spots in that hot spot activity is known to depend on a specific DNA sequence, the heptamer 5Ј-ATGACGT-3Ј, the first T in the heptamer sequence being the site of mut...

Global Analysis of the Relationship between the Binding of the Bas1p Transcription Factor and Meiosis-Specific Double-Strand DNA Breaks in Saccharomyces cerevisiae

“…It is likely that both global and local controls are exerted by chromatin modifications, with the suppressing modifications being dominant. This type of model is consistent with the observation that hot spots moved to a novel chromosome context are often not hot spots (20).…”

Natural Meiotic Recombination Hot Spots in the Schizosaccharomyces pombe Genome Successfully Predicted from the Simple Sequence Motif M26

“…When no other mutations were present, we observed approximately 3,700 cds1 ϩ recombinants per million viable spores. This frequency of recombination is comparable to that observed for the ade6-M26 hot spot (12,17), which shows about the same frequency of meiotic DSBs (31). When M26 ES -I3 was also mutated in both parent strains by a single base pair change (cds1-2), the frequency of recombinants dropped 13-fold.…”

“…This sequence is at least part of the binding site for a heterodimeric transcription factor, Atf1-Pcr1, which is also essential for M26 hot spot activity (22,36). When created by mutation of 1 to 4 bp, the M26 heptamer generates hot spots at multiple positions within the ade6 and ura4 genes (12), and all of those sites tested stimulate the formation of Rec12-dependent meiosis-specific DSBs near the site of the M26 heptamer (31). In addition to M26, Fox et al (13) showed that a closely related sequence, 5Ј-TGACGT C / A -3Ј, termed CRE (cyclic AMP response element), is also an Atf1-Pcr1-dependent hot spot at one site within the ade6 gene.…”

Regulation of the Mts1-Mts2-Dependentade6-M26 Meiotic Recombination Hot Spot and Developmental Decisions by the Spc1 Mitogen-Activated Protein Kinase of Fission Yeast

“…As for transcriptional enhancers, the M26 site functions in a position-and orientation-independent fashion; each of eight M26 sites created by mutagenesis of one or a few base pairs has hot spot activity (11,14,31,41). Furthermore, while basal recombination does not require the Mts1-Mts2 heterodimer (Table 2) (20), hot spot activation does require components of the basal recombination machinery.…”