Y(-TYPE CATIONIC AMINO-ACID-TRANSPORT - EXPRESSION AND REGULATION OF THE MCAT GENES())

The transport of cationic amino acids across animal cell membranes is largely mediated by a small group of well-described transport systems (y(+), b(0,+), B-0,B-+). Only recently have genes encoding transport p roteins in some of these systems been isolated. Two genes, mCAT-1 and mCAT-2, encode related multiple membrane-spanning proteins that share substantial amino acid sequence identity and virtually superimposable hydrophilicity profiles. mCAT-1 and mCAT-2 proteins expressed in Xenop us oocytes are functionally indistinguishable and similar to transport system y(+), but have distinct tissue distribution patterns. mCAT-1 e xpression is nearly ubiquitious and produces a single protein, while m CAT-2 is highly tissue-specific, has two distinct protein isoforms enc oded by a single gene and is expressed in different tissues using at l east two widely separated promoters. All three proteins facilitate the ion-independent transport of arginine, lysine and ornithine. Both mCA T-1 and mCAT-2 proteins have low amino acid sequence similarity but st rikingly similar hydrophilicity profiles with amino acid antiporters, uniporters and symporters of yeast, fungi and eubacteria. Current work will elucidate whether any of the mCAT proteins interact with members of a newly identified family of single membrane-spanning proteins, su ch as rBAT, 4F2 and NAA-Tr, which are thought to modulate or activate y(+)L and/or b(0,+) transport systems.