Transcriptional Induction by Aromatic Amino Acids in Saccharomyces cerevisiae

Abstract

Aromatic aminotransferase II, product of the ARO9 gene, catalyzes the first step of tryptophan, phenylalanine, and tyrosine catabolism in Saccharomyces cerevisiae. ARO9 expression is under the dual control of specific induction and nitrogen source regulation. We have here identified UAS_aro, a 36-bp upstream element necessary and sufficient to promote transcriptional induction of reporter gene expression in response to tryptophan, phenylalanine, or tyrosine. We then isolated mutants in which UAS_aro-mediated ARO9 transcription is partially or totally impaired. Mutations abolishing ARO9 induction affect a gene called ARO80(YDR421w), coding for a Zn₂Cys₆ family transcription factor. A sequence highly similar to UAS_aro was found upstream from the YDR380w gene encoding a homolog of bacterial indolepyruvate decarboxylase. In yeast, this enzyme is postulated to catalyze the second step of tryptophan catabolism to tryptophol. We show that ARO9 and YDR380w(named ARO10) have similar patterns of transcriptional regulation and are both under the positive control of Aro80p. Nitrogen regulation of ARO9 expression seems not directly to involve the general factor Ure2p, Gln3p, Nil1p, Uga43p, or Gzf3p.ARO9 expression appears, rather, to be mainly regulated by inducer exclusion. Finally, we show that Gap1p, the general amino acid permease, and Wap1p (Ycl025p), a newly discovered inducible amino acid permease with broad specificity, are the main aromatic amino acid transporters for catabolic purposes.

ACKNOWLEDGMENTS

We are grateful to S. Soussi-Boudekou for the gift of strains prior to publication, to K. Broman for help in writing the manuscript, and to the members of the laboratory for fruitful discussions.

This work was supported by Medical Scientific Research Fund grant 3.4602.94 (FRSM, Belgium) and by a research grant from the Université Libre de Bruxelles. During this work, I.I. was the recipient of a predoctoral fellowship from the CommunautéFrançaise de Belgique and then from the Fondation Universitaire David et Alice Van Buuren.