THE M26 HOTSPOT OF SCHIZOSACCHAROMYCES-POMBE STIMULATES MEIOTIC ECTOPIC RECOMBINATION AND CHROMOSOMAL REARRANGEMENTS

Homologous recombination is increased during meiosis between DNA seque nces at the same chromosomal position (allelic recombination) and at d ifferent chromosomal positions (ectopic recombination). Recombination hotspots are important elements in controlling meiotic allelic recombi nation. We have used artificially dispersed copies of the ade6 gene in Schizosaccharomyces pombe to study hotspot activity in meiotic ectopi c recombination. Ectopic recombination was reduced 10-1000-fold relati ve to allelic recombination, and was similar to the low frequency of e ctopic recombination between naturally repeated sequences in S. pombe. The M26 hotspot was active in ectopic recombination in some, but not all, integration sites, with the same pattern of activity and inactivi ty in ectopic and allelic recombination. Crossing over in ectopic reco mbination, resulting in chromosomal rearrangements, was associated wit h 35-60% of recombination events and was stimulated 12-fold by M26. Th ese results suggest overlap in the mechanisms of ectopic and allelic r ecombination and indicate that hotspots can stimulate chromosomal rear rangements.