CLONING AND EXPRESSION OF A HUMAN NEUTRAL AMINO-ACID TRANSPORTER WITHSTRUCTURAL SIMILARITY TO THE GLUTAMATE TRANSPORTER GENE FAMILY

A cDNA was isolated from human brain that encodes an amino acid sequen ce 34-39% identical to previously published glutamate transporter sequ ences. Injection of RNA transcribed from this cDNA into Xenopus oocyte s resulted in expression of a transport activity with the properties o f the neutral amino acid uptake system ASC. Superfusion of alanine, se rine, and cysteine evoked sodium-dependent inward currents in voltage- clamped oocytes expressing the transporter. These currents were dose-d ependent, stereospecific, and saturable, with K(m) values ranging from 29 to 88 muM. Northern blot analyses revealed ubiquitous expression o f this gene, termed ASCT1, consistent with the general metabolic role ascribed to system ASC.