Physiological control of repressible acid phosphatase gene transcripts in Saccharomyces cerevisiae

We have examined the regulation of repressible acid phosphatase (APase; orthophosphoric-monoester phosphohydrolase [acid optimum], EC 3.1.3.2) in Saccharomyces cerevisiae at the physiological and molecular levels, through a series of repression and derepression experiments. We demonstrated that APase synthesis is tightly regulated throughout the growth phase and is influenced by exogenous and endogenous Pi pools. During growth in a nonlimiting Pi medium, APase is repressed. When external Pi becomes limiting, there is a biphasic appearance of APase mRNA and enzyme. Our data on APase mRNA half-lives and on the flux of intracellular Pi and polyphosphate during derepression are consistent with a mechanism of transcriptional autoregulation for the biphasic appearance of APase mRNA. Accordingly, preculture concentrations of Pi control the level of corepressor generated from intracellular polyphosphate degradation. When cells are fully derepressed, APase mRNA levels are constant, and the maximal linear accumulation rate of APase is observed. A scheme to integrate phosphorus metabolism and phosphatase regulation in S. cerevisiae is proposed.