Novel genetic components controlling invertase production in Saccharomyces cerevisiae.

Low levels of invertase (EC 3.2.1.26) activity were observed in most diploid strains of S. cerevisiae used in this work. There was no effect of mating type on invertase levels, and cell surface was not a limiting factor, because an increase in ploidy did not cause further decrease in specific invertase activity. Finally, some diploids showed the activity expected from the additive effects of different SUC genes, and haploid strains possessing two SUC genes expressed very variable invertase activities depending on the strain. This suggested the existence of one or more additional genes which control the levels of invertase. Genetic analysis of SUC5 strains provided evidence of the existence of a new gene, RPS5, which drastically reduced the specific invertase activity in strains possessing active SUC alleles. The recessive allele of this gene (rps5) allows expression of higher levels of invertase. We suggest that genes similar RPS5 are responsible for the low levels of invertase activity observed in diploid strains of S. cerevisiae.