Molecular polymorphism of β-fructosidase SUC genes in the Saccharomyces yeasts

The molecular polymorphism of SUC genes that encode beta-fructosidase has been investigated in the yeast genus Saccharomyces. We have determined the nucleotide sequences of subtelomeric SUC3, SUC5, SUC7, SUC8, SUC9, and SUC10 genes of S. cerevisiae and the SUCa gene of S. arboricola. Comparisons of the nucleotide sequences of all known SUC genes revealed the predominance of C -> T transitions in the third codon position, which were silent. The amino acid sequences of beta-fructosidases studied have identity of 88-100%. SUCa (S. arboricola) and SUCb (S. bayanus) proteins, which had amino acid identity with other SUC proteins of less than 92%, were the most divergent. It was determined that accumulation of the polymeric SUC genes takes place in industrial populations of S. cerevisiae, while the other Saccharomyces species (S. arboricola, S. bayanus, S. cariocanus, S. kudriavzevii, S. mikatae, and S. paradoxus) each harbor only one SUC gene. Subtelomeric repeats of beta-fructosidase SUC genes could appear in the genome of S. cerevisiae under the effect of selection in the course of their domestication.