THE DUAL ROLE OF MESSENGER-RNA HALF-LIVES IN THE EXPRESSION OF THE YEAST ALG7 GENE

The yeast ALG7 gene functions by initiating the synthesis of the dolic hol-linked oligosaccharide precursor and plays an important role in th e control oi. protein N-glycosylation, The levels of ALG7 multiple tra nscripts are modulated by the physiological status of the cell and env ironmental cues, and deregulation of their abundance is deleterious to several cellular functions. Since ALG7 mRNAs are unstable, we investi gated the role of these transcripts' half-lives in determining their s teady-state levels. Using a temperature-sensitive RNA polymerase II mu tant, we demonstrate that increased stability was the primary determin ant of higher ALG7 mRNA abundance in response to glucose limitation or treatment with tunicamycin. In contrast, at the G(1)/G(0) transition point, changes in the decay rates were inversely related to ALG7 trans cript accumulation: the decreased abundance of ALG7 mRNAs following ex it from the mitotic cycle was associated with lengthening of the decay rates, while their increased accumulation after growth stimulation co rrelated with decreased stability. This suggests that, depending on th e circumstance, mRNA half-lives can either directly determine the leve l of ALG7 transcript accumulation or oppose regulatory changes at othe r control levels.