EXPRESSION CLONING IN YEAST OF A CDNA-ENCODING A BROAD-SPECIFICITY AMINO-ACID PERMEASE FROM ARABIDOPSIS-THALIANA

To study amino acid transport in plants at the molecular level, we hav e isolated an amino acid permease cDNA from Arabidopsis thaliana by co mplementation of a yeast mutant defective in proline uptake with a cDN A. The predicted polypeptide of 53 kDa is highly hydrophobic with 12 p utative membrane-spanning regions and shows no significant homologies to other known transporters. Expression of the cDNA enables the yeast mutant to take up L-[C-14]proline. Competition studies argue for a bro ad but stereospecific substrate recognition by the permease, which res embles neutral or general amino acid transport systems from Chlorella and higher plants. Both pH dependence and inhibition by protonophores are consistent with a proton symport mechanism.