GENETIC-VARIATION OF THE REPEATED MAL LOCI IN NATURAL-POPULATIONS OF SACCHAROMYCES-CEREVISIAE AND SACCHAROMYCES-PARADOXUS

In Saccharomyces cerevisiae, the gene functions required to ferment th e disaccharide maltose are encoded by the MAL loci. Any one of five hi ghly sequence homologous MAL loci identified in various S. cerevisiae strains (called MAL1, 2, 3, 4 and 6) is sufficient to ferment maltose. Each is a complex of three genes encoding maltose permease, maltase a nd a transcription activator. This family of loci maps to telomere-lin ked positions on different chromosomes and most natural strains contai n more than one MAL locus. A number of naturally occurring, mutant all eles of MAL1 and MAL3 have been characterized which lack one or more o f the gene functions encoded by the fully functional MAL loci. Loss of these gene functions appears to have resulted from mutation and/or re arrangement within the locus. Studies to date concentrated on the stan dard maltose fermenting strains of S. cerevisiae available from the Be rkeley Yeast Stock Center collection. In this report we extend our gen etic analysis of the MAL loci to a number of maltose fermenting and no nfermenting natural strains of S. cerevisiae and Saccharomyces paradox us. No new MAL loci were discovered but several new mutant alleles of MAL1 were identified. The evolution of this gene family is discussed.