ANALYSIS OF A RECOMBINATION HOTSPOT FOR GENE CONVERSION OCCURRING AT THE HIS2 GENE OF SACCHAROMYCES-CEREVISIAE

The properties of gene conversion as measured in fungi that generate a sci containing all the products of meiosis imply that meiotic recombin ation initiates at specific sites. The HIS2 gene of Saccharomyces cere visiae displays a high frequency of gene conversion, indicating that i t is a recombination hotspot. The HIS2 gene was cloned and sequenced, and the cloned DNA was used to make several different types of alterat ions in the yeast chromosome by transformation; these alterations were used to determine the location of the sequences necessary for the hig h levels of meiotic conversion observed at HIS2. Previous work indicat ed that the gene conversion polarity gradient is high at the 3' end of the gene, and that the promoter of the gene is not necessary for the high frequency of conversion observed. Data presented here suggest tha t at least some of the sequences necessary for high levels of conversi on at HIS2 are located over 700 bp downstream of the end of the coding region, extend over (at least) several hundred base pairs, and may be quite complex, perhaps involving chromatin structure. Additional data indicate that multiple single base heterologies within a l-kb interva l contribute Little to the frequency of gene conversion. This contrast s with other reports about the role of heterologies at the MAT locus.