Stronger purifying selection against gene conversions in a pathogenic Saccharomyces cerevisiae strain

Gene conversions most often have no selective impact, but some are selectively disadvantageous whereas others are selectively advantageous. Although gene conversions have been extensively studied in yeasts, very little is known about their selective impact in pathological yeasts. Here, we used the GENECONV software to compare the characteristics of candidate gene conversions found in a pathogenic strain (YJM789) and a nonpathogenic strain (S288c) of Saccharomyces cerevisiae. Interestingly, the pathogenic strain has fewer gene conversions when compared with the nonpathogenic strain. Of the 123 conversions we identified, 27 were identical or similar between the two strains, 62 were specific to the S288c strain, and 34 were specific to the YJM789 strain. Identical and similar conversions likely represent conversions that are under similar levels of purifying selection in both strains. The lower number of gene conversions in most gene families of the pathogenic strain is likely the result of higher purifying selection in this strain. In contrast, the higher number of conversions found in the YRF1 helicase gene family of the pathogenic strain could represent an example of adaptive gene conversions involved in maintaining its telomeres.