Novel function of transcription factor Uga3 as an activator of branched-chain amino acid permease BAP2 gene expression

Gene regulation in yeast occurs at the transcription level, i.e. the basal level of expression is very low and increased transcription requires gene-specific transcription factors allowing the recruitment of basal transcriptional machinery. Saccharomyces cerevisiae BAP2 gene encodes the permease responsible for most uptake of leucine, valine and isoleucine, amino acids that this yeast can use as nitrogen sources. Moreover, BAP2 expression is known to be induced by the presence of amino acids such as leucine. In this context, the results presented in this paper show that BAP2 is an inducible gene in the presence of nitrogen-non-preferred source proline but exhibits high constitutive non-inducible expression in nitrogen-preferred source ammonium. BAP2 expression is regulated by the SPS sensor system and transcription factors Leu3, Gcn4 and Dal81. This can be achieved or not through a direct binding to the promoter depending on the quality of the nitrogen source. We further demonstrate here that an interaction occurs in vivo between Uga3 ‒ the transcriptional activator responsible for γ-aminobutyric acid (GABA)-dependent induction of the GABA genes ‒ and the regulatory region of the BAP2 gene, which leads to an increase in BAP2 transcription.