Changes in membrane proteins associated with inhibition of the general amino acid permease of yeast (Saccharomyces cerevisiae).
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ABSTRACT:
SUBMITTER: Woodward JR
PROVIDER: S-EPMC1163026 | biostudies-other | 1981 May
REPOSITORIES: biostudies-other
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Project description:Cells of the wild-type yeast (Saccharomyces cerevisiae) strain Y185, grown under conditions that de-repress the formation of a general amino acid permease ('Gap') system, bind delta-N-chloroacetyl[1-(14)C]ornithine; L- and D-amino acid substrates of the general amino acid permease system protect against this binding. The protein responsible is released from the cells by homogenization or by preparation of protoplasts; it is not released by osmotic shock. This protein is virtually absent from the wild-type strain when it is grown under conditions that repress the general amino acid permease system, and is also absent from a Gap- mutant Y185-His3, selected by its resistance to D-amino acids. This mutant and repressed wild-type cells also fail to form a number of membrane proteins elaborated by de-repressed wild-type cells. It is possible that all these proteins are components of the general amino acid permease system.
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Project description:Amino acids are essential metabolites but can also be toxic when present at high levels intracellularly. Substrate-induced downregulation of amino acid transporters in Saccharomyces cerevisiae is thought to be a mechanism to avoid this toxicity. It has been shown that unregulated uptake by the general amino acid permease Gap1 causes cells to become sensitive to amino acids. Here, we show that overexpression of eight other amino acid transporters (Agp1, Bap2, Can1, Dip5, Gnp1, Lyp1, Put4, or Tat2) also induces a growth defect when specific single amino acids are present at concentrations of 0.5-5 mM. We can now state that all proteinogenic amino acids, as well as the important metabolite ornithine, are growth inhibitory to S. cerevisiae when transported into the cell at high enough levels. Measurements of initial transport rates and cytosolic pH show that toxicity is due to amino acid accumulation and not to the influx of co-transported protons. The amino acid sensitivity phenotype is a useful tool that reports on the in vivo activity of transporters and has allowed us to identify new transporter-specific substrates.
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