Differential regulation of STA genes of Saccharomyces cerevisiae

Abstract

The single glucoamylase gene ( SGA 1) of the yeast Saccharomyces cerevisiae is expressed exclusively during the sporulation phase of the life cycle. Enzymatic studies and nucleic acid sequence comparisons have shown that the SGA 1 glucoamylase is closely related to the secreted enzymes of S. cerevisiae var. diastaticus . The latter are encoded by any of three unlinked STA genes, which have been proposed to derive from the ancestral SGA 1 form by genomic rearrangement. We show that the regulation of SGA 1 is distinct from that of the other members of the STA gene family. SGA 1 expression did not respond to STA 10, the primary determinant of glucoamylase expression from STA 2. Unlike STA 2, SGA 1 was not regulated directly by the mating type locus. Expression of SGA1 depended on the function of the MAT products in supporting sporulation and not on the formation of haploid progeny spores or on the composition of the mating type locus per se. We conclude that the STA genes acquired regulation by STA 10 and MAT by the genomic rearrangements that led to their formation. This regulation is thus distinct from that of the ancestral SGA 1 gene.