UGA4 gene encoding the γ-aminobutyric acid permease in Saccharomyces cerevisiae is an acid-expressed gene

Abstract

Background and aims: biological processes in all organisms are controlled by environmental conditions, however, information concerning the molecular responses to external pH is scarce. In this work we studied the pH response of UGA4 gene encoding -aminolevulinic acid and -aminobutyric acid permease in Saccharomyces cere isiae. Methods: we analyzed the effect of pH on the expression of UGA4 gene measuring -galactosidase activity in cells carrying a UGA4::lacZ fusion gene. Results: results indicate that UGA4 expression is higher at acidic pH. The expression of UGA3 and UGA35 genes, which encode two positive transcription factors, is not regulated by external pH, while the expression of UGA43 gene encoding a repressor of UGA4 transcription is dependent on pH. Using a strain lacking Uga43p we clearly showed that the effect of ambient pH on UGA4 expression is not a secondary effect of the pH regulation on UGA43. We have also demonstrated that the effect of pH can only be detected when UGA4 gene is not subject to a strong repression by Uga43p nor to GABA induction. Conclusion: here, we demonstrate that UGA4 is an acid-expressed gene. This regulation is probably mediated by Rim101p through the consensus site 5-GCCARG-3 at 237 bp preceding the UGA4 coding sequence.