PTR3, A NOVEL GENE MEDIATING AMINO ACID-INDUCIBLE REGULATION OF PEPTIDE-TRANSPORT IN SACCHAROMYCES-CEREVISIAE

We have isolated and characterized the Saccharomyces cerevisiae PTR3 g ene by functional complementation of a mutant deficient for amino acid -inducible peptide transport. PTR3 is predicted to encode a protein of 678 amino acids that exhibits no similarity to any other protein in t he database. Deletion of the PTR3 open reading frame pleiotropically r educed the sensitivity to toxic peptides and amino acid analogues. Ini tial rates of radiolabelled dipeptide uptake demonstrated that elimina tion of PTR3 resulted in the loss of amino acid-induced levels of pept ide transport. PTR3 was required for amino acid-induced expression of PTR2, the gene encoding the dipeptide/tripeptide transport protein, bu t was not necessary for nitrogen catabolite repression of peptide impo rt or PTR2 expression. It was determined that PTR3 also modulates expr ession of BAP2, the gene encoding the branched-amino acid permease. Fu rthermore, we present genetic evidence that suggests that PTR3 functio ns within a novel regulatory pathway that facilitates amino acid induc tion of the PTR system.