THE POSTTRANSLATIONAL MODIFICATION OF PHOSPHOGLUCOMUTASE IS REGULATEDBY GALACTOSE INDUCTION AND GLUCOSE REPRESSION IN SACCHAROMYCES-CEREVISIAE

The enzyme phosphoglucomutase functions at a key point in carbohydrate metabolism. In this paper, we show that the synthesis of the major is oform of yeast phosphoglucomutase, encoded by the GAL5 (PGM2) gene, is regulated in a manner that is distinct from that previously described for other enzymes involved in galactose metabolism in the yeast Sacch aromyces cerevisiae. Accumulation of this isoform increased four- to s ixfold when the culture experienced either glucose depletion or heat s hock. However, heat shock induction did not occur unless the cells wer e under glucose repression. This nonadditive increase in expression su ggests that the regulatory mechanisms controlling the heat shock induc tion and glucose repression of the GAL5 gene are functionally related. We previously demonstrated that phosphoglucomutase is modified by a p osttranslational Glc-phosphorylation reaction, We now show that this p osttranslational modification, like phosphoglucomutase expression itse lf, is also regulated by galactose induction and glucose repression, F inally, no evidence was found to indicate that the Glc-phosphorylation of phosphoglucomutase alters its enzymatic activity under the conditi ons examined.