Regulation of pyc1 encoding pyruvate carboxylase isozyme I by nitrogen sources in Saccharomyces cerevisiae

Abstract

In Saccharomyces cerevisiae, the existence of PYC1 and PYC2 encoding cytosolic pyruvate carboxylase isoform I and II is rather puzzling, owing to the lack of potent differential gene regulation by the carbon sources. We report several findings indicating that these two genes are differentially regulated by the nature of the nitrogen source. In wild-type cells, the activity of pyruvate carboxylase, which is the sum of pyruvate carboxylase isoform I and II, was two-to fivefold lower in carbon medium containing aspartate, asparagine, glutamate or glutamine instead of ammonium as the nitrogen source, whereas it was 1.5-to threefold higher when the ammonium source was substituted by arginine, methionine, threonine or leucine. These enzymatic changes were independent of the nature of the carbon source and closely correlated to the changes in b-galactosidase from PYC1-lacZ gene fusion and in PYC1 transcripts. Transfer of exponentially growing cells of the pyc2 mutant from an aspartate or a glutamate medium to an ammonium medium caused a fivefold increase in PYC1 mRNA in less than 30 min, whereas in the inverse experiment, PYC1 transcripts returned within 30 min to the low levels found in aspartate/ glutamate medium. By contrast, these conditions affected neither the pyruvate carboxylase activity encoded by PYC2 nor PYC2 mRNA. Considering that changes in PYC1 expression inversely correlated with changes in a-ketoglutarate concentration or in a-ketoglutarate/glutamate ratio following the nitrogen shift experiments, and taking into account the pivotal role of this metabolite in ammonium assimilation, it is suggested that changes in a-ketoglutarate or in the a-ketoglutarate/glutamate ratio might be implicated in triggering the nitrogen effects on PYC1 expression. The physiological significance of the differential sensitivity of PYC1 and PYC2 genes with respect to the nitrogen source in the growth medium is also discussed.

Investigation by 13C-NMR and tricarboxylic acid (TCA) deletion mutant analysis of pathways for succinate formation in Saccharomyces cerevisiae during anaerobic fermentation

“…It remains to be determined whether intracellular 2-OG is the induction signal for enhanced OGDH activity. It has been suggested that intracellular 2-OG concentration may regulate PYC1, encoding one isoform of pyruvate carboxylase (Huet et al, 2000), and might be a key signal for regulation of the retrograde response (RTG)-dependent pathways (Liu & Butow, 1999).…”

Mitochondrial‐morphology‐targeted breeding of industrial yeast strains for alcohol fermentation

“…It has also been reported that overexpression of pyruvate carboxylase, encoded by the gene PYC2 , which is responsible for synthesis of oxaloacetic acid from pyruvic acid, led to an increase in malic acid production in glucose‐limited continuous culture [100]. Furthermore, pyruvate carboxylase activity has been reported to be affected by the concentrations of many substances, such as aspartic acid, asparagine, glutamic acid, glutamine, ammonium, arginine, methionine, threonine or leucine [101], making an exploration of the metabolism of these organic acids even more difficult. Therefore the pathways which were up‐regulated or down‐regulated in the fis1 disruptant, leading to high malate production, remain unknown and open for future study.…”