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

Corresponding author: James R. Broach, Princeton University, Washington Rd., Princeton, NJ 08544., jbroach{at}molbio.princeton.edu (E-mail)

Communicating editor: B. J. ANDREWS

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 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 2 protein in 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 still influenced donor preference in interchromosomal mating-type switching, supporting a role of 2 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.

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