The Saccharomyces cerevisiae Recombination Enhancer Biases Recombination During Interchromosomal Mating-Type Switching but Not in Interchromosomal Homologous Recombination

摘要

Haploid Saccharomyces can change mating type through HO -endonuclease cleavage of an expressor locus, MAT , followed by gene conversion using one of two repository loci, HML or HMR , as donor. The mating type of a cell dictates which repository locus is used as donor, with a cells using HML and α cells using HMR . This preference is established in part by RE , a locus on the left arm of chromosome III that activates the surrounding region, including HML , for recombination in a cells, an activity suppressed by α2 protein in α cells. We have examined the ability of RE to stimulate different forms of interchromosomal recombination. We found that RE exerted an effect on interchromosomal mating-type switching and on intrachromosomal homologous recombination but not on interchromosomal homologous recombination. Also, even in the absence of RE, MAT α still influenced donor preference in interchromosomal mating-type switching, supporting a role of α2 in donor preference independent of RE . These results suggest a model in which RE affects competition between productive and nonproductive recombination outcomes. In interchromosome gene conversion, RE enhances both productive and nonproductive pathways, whereas in intrachromosomal gene conversion and mating-type switching, RE enhances only the productive pathway.