Control-mechanisms acting at the transcriptional and post-transcriptional levels are involved in the synthesis of the arginine pathway carbamoylphosphate synthase of yeast.

Abstract

In Saccharomyces cerevisiae, the synthesis of the arginine pathway enzyme carbamoylphosphate synthase (CPSase A) is subject to two control mechanisms. One mechanism, the general control of amino acid biosynthesis, influences the expression of both CPA1 and CPA2 genes, the structural genes for the two subunits of the enzyme. The second mechanism, the specific control of arginine biosynthesis, only affects the expression of CPA1. To study these mechanisms in more detail, we have cloned the CPA1 and CPA2 genes and used their DNA to measure the CPA1 and CPA2 mRNA content of cells grown under various conditions. A close coordination was observed in the variation of the levels of CPA1 and CPA2 mRNAs and polypeptide products under conditions where the general control of amino acid biosynthesis operates. In contrast, little correlation was found between the levels of CPA1 mRNA and the corresponding protein for conditions affecting repression by arginine: the total amplitude of variation was 6‐fold higher for the CPA1 protein than for the CPA1 messenger transcript. Such findings are consistent with the conclusion that the general control operates at the transcriptional level and that the specific arginine control acts primarily at a post‐transcriptional level.

Arginine restriction induced by delta-N-(phosphonacetyl)-L-ornithine signals increased expression of HIS3, TRP5, CPA1, and CPA2 in Saccharomyces cerevisiae.

“…Both CPA] and CPA2 have been reported to be regulated by general amino acid control (21,27). Strains with leaky mutations in the arginine, histidine, isoleucine-valine, or lysine pathway and grown in the absence of the respective amino acids were shown to have elevated levels of both CPA2 mRNA and synthetase subunit (21,27).…”

“…Both CPA] and CPA2 have been reported to be regulated by general amino acid control (21,27). Strains with leaky mutations in the arginine, histidine, isoleucine-valine, or lysine pathway and grown in the absence of the respective amino acids were shown to have elevated levels of both CPA2 mRNA and synthetase subunit (21,27). Similarly elevated concentrations of CPA] mRNA and protein were also observed in the leaky arginine auxotroph (argJ'-) but not in partial histidine, lysine, or isoleucine-valine auxotrophs (21,27).…”

“…increased transcription of the genes in a leaky arginine auxotroph (argJ'-) (21,27), however, CPAJ and CPA2 have been reported to be under general amino acid control. Since the argJ'-mutation complements all known mutants in the arginine biosynthetic pathway (27), the explanation of the increased levels of arginine biosynthetic enzymes observed in this strain is not entirely clear.…”

Post-transcriptional Expression Regulation in the Yeast Saccharomyces cerevisiae on a Genomic Scale

“…Translation on demand has been suggested for the yeast proteins GCN4, HAC1, ICY2, and CPA1 (23)(24)(25)32). GCN4 has an exceptionally high mRNA abundance but a very low ribosome density.…”

“…The available data thus confirm the notion that these four proteins are subject to translation on demand. For comparison, we have included the median values for the whole cell and the data for CPA2, which likely is not regulated at the translational level (32). In contrast to the other proteins, CPA2 has a very high PRR and a comparably high ribosome density, confirming constitutive expression of CPA2.…”