RESPONSE OF A YEAST GLYCOGEN-SYNTHASE GENE TO STRESS

In the yeast Saccharomyces cerevisiae, glycogen synthase is encoded by two genes: GSY1 and GSY2. The activity of the enzymes increases as cu ltures enter the stationary phase of growth. Using a GSY2::lacZ fusion gene, we have demonstrated that the increase in glycogen synthase act ivity resulted, at least in part, from an increase in the level of the protein rather than simply from a change in its phosphorylation state . Northern blot analysis showed a parallel increase in the level of th e GSY2 mRNA, which is consistent with transcriptional activation of GS Y2. Deletion analysis identified three regions upstream of GSY2 which are involved in GSY2 expression: regions A (-390 to -347 relative to t he start of translation), B (-252 to -209) and C (-209 to -167). Regio n A or C independently activated expression of GSY2. In contrast, regi on B alone yielded only modest expression. Expression of GSY2 is induc ed by growth to stationary phase, heat shock or nitrogen starvation. R esponse to these stressors is mediated by elements within regions A an d C. These elements appear to be related to the stress-response elemen ts found in other stress-responsive genes.