Allele Diversity among Genes of the Sulfate Reduction Pathway in Wine Strains ofSaccharomyces cerevisiae

Abstract

Genes encoding enzymes of the sulfate reduction pathway in <i>Saccharomyces cerevisiae</i> immediately downstream of sulfite reductase, <i>MET6</i>, <i>MET17</i>, and <i>CYS4</i>, were sequenced in 12 wine isolates of this yeast. The <i>MET17</i> alleles were identical in sequence to each other and to the sequence of the standard laboratory strain, S288C. For one additional commercial strain, a disruption of one of the <i>MET17</i> alleles was found, but the other allele was identical to the consensus sequence. All 12 strains showed the identical five neutral base pair changes in <i>CYS4</i> sequence when compared to the sequence reported for S288C. One strain contained an additional base pair change that led to an amino acid change. Two neutral base pair changes were observed in the sequences of <i>MET6</i> for one wine yeast strain and three other strains had changes in sequence that were not neutral and altered the amino acid sequence. Regulatory regions upstream of these genes were also sequenced for a subset of strains. Several differences in noncoding regions were found, a few of which resulted in changes in putative transcription factor binding sites. Genes encoding different alleles were used to transform a corresponding null mutation of S288C and enzyme activity and hydrogen sulfide production evaluated. The <i>CYS4</i>^UCD932 allele resulted in faster fermentation rates and reduced hydrogen sulfide production when compared with the same strain transformed with <i>CYS4</i>^S288C. The <i>MET6</i> alleles showed no effects on sulfide formation in a null background.