Expression cloning of a Na(+)-independent neutral amino acid transporter from rat kidney.

Uptake of long-chain and aromatic neutral amino acids into cells is known to be catalyzed by the Na(+)-independent system L transporter, which is ubiquitous in animal cells and tissues. We have used a Xenopus oocyte expression system to clone the cDNA of a system L transporter from a rat kidney cDNA library. The 2.3-kilobase cDNA codes for a protein of 683 amino acids. The transporter has four putative membrane-spanning domains and bears no sequence or structural homology to any known animal or bacterial transporter. When transcribed and expressed in Xenopus oocytes, the transporter exhibits many, but not all, of the characteristics of L-system transporters, suggesting that this represents one of several related L-system transporters.