Regulation of arginine metabolism in Saccharomyces cerevisiae: a network of specific and pleiotropic proteins in response to multiple environmental signals

In Saccharomyces cerevisiae, the expression of the genes involved in the sy nthesis and degradation of arginine is modulated by multiple specific and p leiotropic factors, acting as repressors or activators as a function of the availability of amino acids, of nitrogen source, and the presence or absen ce of arginine. Four proteins (Arg80, Arg81, Mcm1 and Arg82) coordinate the expression of arginine metabolic genes, by repressing the biosynthetic gen es and by inducing the catabolic genes, in response to arginine. Arg80, Arg 81 and Mcm1 form a complex interacting with DNA sequences called >>arginine boxes<< present in the promoters of arginine co-regulated genes. Binding o f arginine to Arg81 allows the interaction of the complex with DNA. The rol e of Arg82 is to stabilize the Mcm1 and Arg80 proteins. The synthesis of on e of the subunits of carbamoylphosphate synthetase encoded by CPA1 gene is also repressed by arginine. However, this results from a translational cont rol involving a 25 amino acid peptide encoded by the messenger of CPA1. Exp ression of the catabolic genes CAR1 and CAR2 is repressed, as long as exoge nous nitrogen is available, by the regulatory complex Ume6-Sin3-Rpd3 exhibi ting histone deacetylase activity. Expression of CAR1 but not of CAR2 is ac tivated by Gln3 and Nil1 when cells are grown on poor nitrogen sources.