ACTIVE AND INACTIVE TRANSPLACEMENT OF THE M26 RECOMBINATION HOTSPOT IN SCHIZOSACCHAROMYCES-POMBE

The ade6-M26 mutation of the fission yeast Schizosaccharomyces pombe c reates a meiotic recombination hotspot that elevates ade6 intragenic r ecombination similar to 10-15-fold. A heptanucleotide sequence includi ng the M26 point mutation is required but not sufficient for hotspot a ctivity. We studied the effects of plasmid and chromosomal context on M26 hotspot activity. The M26 hotspot was inactive on a multicopy plas mid containing M26 embedded within 3.0 or 5.9 kb of ade6 DNA. Random S . pombe genomic fragments totaling similar to 7 Mb did not activate th e M26 hotspot on a plasmid. M26 hotspot activity was maintained when 3 .0-, 4.4-, and 5.9-kb ade6-M26 DNA fragments, with various amounts of non-S. pombe plasmid DNA, were integrated at the ura4 chromosomal locu s, but only in certain configurations relative to the ura4 gene and th e cointegrated plasmid DNA. Several integrations created new M26-indep endent recombination hotspots. In all cases the non-ade6 DNA was locat ed >1 kb from the M26 site, and in some cases >2 kb. Because the chrom osomal context effect was transmitted over large distances, and did no t appear to be mediated by a single discrete DNA sequence element, we infer that the local chromatin structure has a pronounced effect on M2 6 hotspot activity.