Differential intrachromosomal hyper-recombination phenotype of spt4 and spt6 mutants of S. cerevisiae.

In order to test whether mutations affecting transcription also affect DNA recombination, we have determined the influence of a number of snf/swi and spt/sin transcriptional regulatory mutations on the recombination of a DNA inverted repeat. Among the nine different mutations analyzed, we found that spt4 and spt6 confer a significant hyper-recombination phenotype. Both mutations produced increases in the frequencies of reciprocal exchange/gene conversion and deletion events ranging from 1- to 15-fold above the wild-type levels, as determined in six direct repeat systems and one inverted repeat. The frequency of mitotic recombination between homologs, determined at one chromosomal locus, was not affected. We discuss the intrachromosomal hyper-recombination phenotype of spt4 an spt6 on the basis of the possible functions of SPT4 and SPT6 on transcriptional regulation and on chromatin structure.