Carbon Catabolite Repression Regulates Amino Acid Permeases in Saccharomyces cerevisiae via the TOR Signaling Pathway

We have identified carbon catabolite repression (CCR) as a regulator of amino acid permeases in Saccharomyces cerevisiae, elucidated the permeases regulated by CCR, and identified the mechanisms involved in amino acid permease regulation by CCR. Transport of l-arginine and l-leucine was increased by ∼10–25-fold in yeast grown in carbon sources alternate to glucose, indicating regulation by CCR. In wild type yeast the uptake (pmol/106 cells/h), in glucose versus galactose medium, of l-[14C]arginine was (0.24 ± 0.04 versus 6.11 ± 0.42) and l-[14C]leucine was (0.30 ± 0.02 versus 3.60 ± 0.50). The increase in amino acid uptake was maintained when galactose was replaced with glycerol. Deletion of gap1Δ and agp1Δ from the wild type strain did not alter CCR induced increase in l-leucine uptake; however, deletion of further amino acid permeases reduced the increase in l-leucine uptake in the following manner: 36% (gnp1Δ), 62% (bap2Δ), 83% (Δ(bap2-tat1)). Direct immunofluorescence showed large increases in the expression of Gnp1 and Bap2 proteins when grown in galactose compared with glucose medium. By extending the functional genomic approach to include major nutritional transducers of CCR in yeast, we concluded that SNF/MIG, GCN, or PSK pathways were not involved in the regulation of amino acid permeases by CCR. Strikingly, the deletion of TOR1, which regulates cellular response to changes in nitrogen availability, from the wild type strain abolished the CCR-induced amino acid uptake. Our results provide novel insights into the regulation of yeast amino acid permeases and signaling mechanisms involved in this regulation.