DIP5P MEDIATES HIGH-AFFINITY AND HIGH-CAPACITY TRANSPORT OF L-GLUTAMATE AND L-ASPARTATE IN SACCHAROMYCES-CEREVISIAE

Genes encoding homologues of known aminoacid permeases were deleted in a strain also deficient in the general amino-acid permease. The uptak e capacity of the mutants was investigated for several L-alpha-amino a cids. Deletion of a gene denoted DIP5 results in the loss of L-asparta te and L-glutamate uptake. The dip5 mutation caused a several hundred- fold reduction of uptake of the two amino acids, both in cells grown o n proline as a nitrogen source and in cells grown on ammonium. DIP5-de pendent uptake of L-aspartate and L-glutamate was somewhat lower in am monium-grown cells than in proline-grown cells. Transcriptional regula tion is at least partially responsible for this difference, as shown b y assaying the DIP5 promoter fused to lacZ. This suggests that the pro moter is subject to nitrogen catabolite repression. Transport of a few other amino acids was moderately affected by dip5 but was not compete d by L-aspartate in the DIP5 parental strain: transport of these amino acids is therefore unlikely to be mediated by Dip5p. Our results sugg est that DIP5 encodes an amino-acid permease with a high transport cap acity and a high affinity for L-glutamate and L-aspartate, with a K-t of about 50 mu M for both.