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

Background and aims: biological processes in all organisms are controlled b y environmental conditions, however, information concerning the molecular r esponses to external pH is scarce. In this work we studied the pH response of UGA4 gene encoding delta -aminolevulinic acid and gamma -aminobutyric ac id permease in Saccharomyces cerevisiae. Methods: we analyzed the effect of pH on the expression of UGA4 gene measuring beta -galactosidase activity i n cells carrying a UGA4::lacZ fusion gene. Results: results indicate that U GA4 expression is higher at acidic pH. The expression of UGA3 and UGA35 gen es. which encode two positive transcription factors, is not regulated by ex ternal 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 ef fect of pH can only be detected when UGA4 gene is not subject to a strong r epression 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 (201). (C) 2001 Elsevier Science Ltd. All rights reser ved.