Characterization of AAT1: a gene involved in the regulation of amino acid transport in Saccharomyces cerevisiae.

A new class of Saccharomyces cerevisiae mutants (aat1 - amino acid transport) has been identified. These mutants are unable to grow on rich medium or on minimal medium supplemented with certain amino acids (isoleucine, methionine, phenylalanine, tyrosine or valine). This phenotype is directly linked to the presence of the leu2 allele in these strains: aat1 LEU2 organisms grow normally on all media tested. Leucine uptake through the leucine-specific permease is inhibited to less than 35% of wild-type levels in aat1 cells preincubated in nonpermissive media, and the activity of the general amino acid permease is also low in these conditions. aat1 cells are therefore unable to grow on rich media because they cannot take up enough leucine to supplement their auxotrophic requirement.