CHARACTERIZATION OF SACCHAROMYCES-CEREVISIAE ARO8 AND ARO9 GENES ENCODING AROMATIC AMINOTRANSFERASE-I AND AMINOTRANSFERASE-II REVEALS A NEWAMINOTRANSFERASE SUBFAMILY

The ARO8 and ARO9 genes of Saccharomyces cerevisiae were isolated by c omplementation of the phenylalanine/tyrosine auxotrophy of an aro8 aro 9 double-mutant strain that is defective in aromatic aminotransferases I (aro8) and II (aro9). The genes were sequenced, and deletion mutant s were constructed and analysed. The expression of ARO8 and ARO9 was s tudied. The deduced amino acid sequences of Aro8p and Aro9p suggest th at the former is a 500-residue, 56168-Da polypeptide and the latter a 513-residue, 58516-Da polypeptide. They correspond, respectively, to Y g1202p and Yhr137p, two putative proteins of unknown function revealed by systematic sequencing of the yeast genome. We show that aromatic a minotransferases I and II are homologous proteins, members of aminotra nsferase subgroup I, and, together with three other proteins, they con stitute within the subgroup a new subfamily of enzymes specialised for aromatic amino acid and alpha-aminoadipate transamination. ARO8 expre ssion is subject to the general control of amino acid biosynthesis. AR O9 expression is induced when aromatic amino acids are present in the growth medium and also in aro8 mutants grown on minimal ammonia medium . An autonomously replicating sequence (ARS) element is located betwee n the ARO8 gene and YGL201c which encodes a protein of the minichromos ome maintenance family.