SUPERFAMILY OF ALPHA-GALACTOSIDASE MEL GENES OF THE SACCHAROMYCES-SENSU-STRICTO SPECIES COMPLEX

In order to study the molecular evolution of the yeasts grouped in the Saccharomyces sensu stricto species complex by analysis of the MEL ge ne family, we have cloned and sequenced two new species-specific MEL g enes from Saccharomyces yeasts: S. paradoxus (MELp) and a Japanese Sac charomyces sp. (MELj). The clones were identified by sequence homology to the S. cerevisiae MEL1 gene. Both clones revealed an ORF of 1413 b p coding for a protein of 471 amino acids. The deduced molecular weigh ts of the alpha-galactosidase enzymes were 52 767 for MELp and 52 378 for MELj. The nucleotide sequences of the MELp (EMBL accession no. X95 505) and the MELj (EMBL accession no. X95506) genes showed 74.7% ident ity. The degree of identity of MELp to the MEL1 gene was 76.8% and to the S. pastorianus MELx gene, 75.7%. The MELj coding sequence was 75.1 % identical to the MEL1 gene and 80.7% to the MELx gene. The data sugg est that MEL1, MELj, MELp, and MELx genes are species-specific MEL gen es. The strains studied each have only one MEL locus. The MELp gene is located on the S. paradoxus equivalent of S. cerevisiae chromosome X; the MELj gene was on the chromosome that comigrates with the S. cerev isiae chromosome VII/XV doublet and hybridizes to the S. cerevisiae ch romosome XV marker HIS3.