Structure and Regulation of the Multigene Family Controlling Maltose Fermentation in Budding Yeast

Abstract

This chapter describes the structure and regulation of the MAL loci, with particular emphasis on the work conducted in laboratory. Maltose fermentation has four unlinked loci, MALI through MALA, were originally described. Subsequently, three more MAL loci were identified: MAL5 through MAL7. Two of these— namely, MAL5 and MAL7, were later found to encode amylomaltase, MAL5 being allelic to the STAl gene that encodes glucoamylase. The functional MAL loci have been mapped on the following chromosomes: MALl, VII; MAL2, 111; MAL3, 11; MALA, XI; MAL6, VIII. Support for the regulatory-gene model came from the observation that strains carrying different MAL loci produce biochemically indistinguishable maltase enzymes and that although several temperature sensitive mutants that do not ferment maltose had been isolated, none of them displayed temperature-sensitive maltase activity. Subsequently, Naumov showed that two distinct complementation groups, MALp and MALg, were present at the MALl, MAL3, and MALG loci in naturally occurring Mal-strains. The available evidence suggests that MALp is functionally equivalent to the complentation group identified by mutational analysis at the MAL6 locus, and that this gene, designated MALGR, encodes a regulatory protein involved in the coordinate induction of the synthesis of both maltase and maltose permease.