In Saccharomyces cerevisiae, mutations at the GAP1 locus selectively abolish the activity of the general amino acid transport system. This permease catalyses active transport of apparently all biological amino acids across the plasma membrane. We have determined the nucleotide sequence of the GAP1 gene. The sequence contains an open reading frame of 601 codons corresponding to a polypeptide of Mr 65578. This polypeptide is strongly hydrophobic; it exhibits three potential glycosylation sites. Hydropathy analysis suggests 12 membrane-spanning regions. The N-terminal domain is charged, it does not resemble hydrophobic signal sequences found in secreted proteins. Hence the GAP1 gene encodes a protein with characteristics typical of integral membrane proteins translocating ligants across cellular membranes. The deduced amino acid sequence of GAP1 protein presents strong similarities to those of the yeast arginine, histidine and proline permeases, suggesting a common evolutionary origin for these amino acid permeases. Nitrogen-source regulation of the GAP1 permease is believed to occur at two distinct levels, i.e. permease synthesis and permease activity [Grenson (1983) Eur. J. Biochem. 133, 135-139]. Northern analysis of GAP1-specific transcripts in wild-type and in mutant strains is in agreement with these views and indicates that nitrogen catabolite repression of GAP1 synthesis occurs at the RNA level.