Conservation of amino acid transporters in fungi, plants and animals.

When comparing the transporters of three completely sequenced eukaryotic genomes--Saccharomyces cerevisiae, Arabidopsis thaliana and Homo sapiens--transporter types can be distinguished according to phylogeny, substrate spectrum, transport mechanism and cell specificity. The known amino acid transporters belong to five different superfamilies. Two preferentially Na(+)-coupled transporter superfamilies are not represented in the yeast and Arabidopsis genomes, whereas the other three groups, which often function as H(+)-coupled systems, have members in all investigated genomes. Additional superfamilies exist for organellar transport, including mitochondrial and plastidic carriers. When used in combination with phylogenetic analyses, functional comparison might aid our prediction of physiological functions for related but uncharacterized open reading frames.