Characterization of MEL genes in the genus Zygosaccharomyces

We cloned and sequenced a Zygosaccharomyces cidri MEL gene with a view to investigating the structure and regulation of yeast MEL genes. The amino acid sequence deduced from the nucleotide sequence showed 78.6% and 78.2% similarity to Saccharomyces cerevisiae and Saccharomyces pastorianus alpha-galactosidases, respectively. The expression of the MEL gene in several Zygosaccharomyces strains was induced by galactose. An electrophoretic karyotype of several Zygosaccharomyces species was obtained using contour-clamped electric field gel electrophoresis. The minimum number of chromosomes was five for Z. cidri, six for Z. fermentati, three for Z. florentinus, and four for Z. microellipsoides. The sizes of the chromosomes were generally larger than those of S. cerevisiae, the smallest containing approximately 0.4 megabase. The MEL gene was located, using the Z. cidri MEL gene as a probe, on the largest chromosome of the Z. cidri strains. In addition, a smaller chromosome (600 kb) in Z. cidri strain CBS4575 showed hybridization to the homologous MEL probe. This chromosome was absent in Z. cidri strain CBS5666. The probe hybridized to the largest chromosome of Mel+ Z. fermentati strains but failed to hybridize to any chromosome of Mel+ Z. mrakii or Z. florentinus strains. These results suggest the existence of a polymorphic MEL gene family in the yeast Zygosaccharomyces.