POSITION-INDEPENDENT AND ORIENTATION-INDEPENDENT ACTIVITY OF THE SCHIZOSACCHAROMYCES-POMBE MEIOTIC RECOMBINATION HOT-SPOT M26

The activity of the M26 meiotic recombination hot spot of Schizosaccha romyces pombe depends on the presence of the heptamer 5'-ATGACGT-3'. T ransplacement of DNA fragments containing the ade6-M26 gene to other c hromosomal loci has previously demonstrated that the heptamer function s in some, but not all, transplacements, suggesting that hot spot acti vity 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 ural gen es, the heptamer was active as a recombination hot spot, in an orienta tion-independent manner, at all locations tested. Thus, the heptamer s equence can create an active hot spot in other chromosomal contexts, p rovided that the gross chromosomal structure is not altered; this resu lt is consistent with the hypothesis that a specific higher-order chro matin structure is required for M26 hot spot activity.