SSU1-R, a sulfite resistance gene of wine yeast, is an allele of SSU1 with a different upstream sequence

A sulfite resistance gene, SSU1-R, was cloned from a highly sulfite-resistant strain of Saccharomyces cerevisiae, Y-9, which was isolated as a contaminant from a wine must. The coding region sequence of SSU1-R was almost identical to that of SSU1, the gene that has been shown to be responsible for sulfite resistance. Although SSU1 is located on chromosome XVI of S. cerevisiae, the upstream region of SSU1-R was homologous with a sequence of chromosome VIII. In our Northern analysis, an intense band was detected in Y-9 and K1-V1116 strains, both of which exhibit strong sulfite resistance, with and without sulfite in the medium. On the other hand, under the same experimental conditions, no band was detected in OC-2, a strain that exhibits weak sulfite resistance. Physical mapping of SSU1/SSU1-R showed that this sequence was on chromosome VIII of Y-9 and the two wine strains, K1-V1116 and WE14. OC-2 and twenty-three other wine, sake, beer, shochu (Japanese distilled liquor), alcohol, bakery, and laboratory strains, had this sequence on chromosome XVI, and four other wine strains had it on both chromosomes. Thus, the difference in the upstream sequence of SSU1/SSU1-R seems to cause differences in the transcription rates and degree of sulfite resistance.