Inhibition of glycogen synthesis in Saccharomyces cerevisiae by the mating pheromone alpha-factor

Treatment of the yeast Saccharomyces cerevisiae with the pheromone alpha-factor caused an inhibition of glycogen synthesis in MATa haploid cells but not in MAT alpha cells or MATa/MAT alpha diploid cells. The concentration of alpha-factor required for a half-maximal inhibition was comparable to that required for the induction of the FUS1 gene. Strains containing a disruption in ste2 or ste12 or temperature-sensitive mutations in ste4, ste7, or ste11 continued to divide and to accumulate glycogen in the presence of alpha-factor. In contrast, inhibition of glycogen occurred upon exposure to mating pheromone of far1 mutants which, under this condition, fail to arrest in G1 and continue to divide while simultaneously undergoing the transcriptional induction and morphological changes typical of mating cells. The inhibition of glycogen accumulation by alpha-factor persisted in a strain lacking glycogen phosphorylase (EC 2.4.1.1), which ruled out the participation of this enzyme in the pheromone response. Glycogen synthase (EC 2.4.1.11) from a cells treated with alpha-factor was found primarily in the glucose 6-phosphate-dependent (inactive) form whereas the total activity was unaltered. This indicates that the action of mating pheromone is mainly to inhibit the interconversion of the inactive glucose 6-phosphate-dependent form to the active glucose 6-phosphate-independent form of glycogen synthase without affecting the concentration of the enzyme.