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

JUAN FACUNDO GULIAS; BERMUDEZ MORETTI MARIANA; JENNIFER VALENCIA GUILLEN; MUÑOZ, SEBASTIÁN ANÍBAL; CORREA GARCIA SUSANA

Salta

Congreso; SAIB; 2019

SAIBMu

Transcription regulation of most genes in yeast occurs at the level of activation, 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 the major part of leucine, valine and isoleucine uptake, 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. However, BAP2 regulation by nitrogen source quality has rendered controversial results and remains unclear. In this context, we analyzed the transcriptional regulation of BAP2 in response to extracellular leucine in the presence of both a poor and a rich nitrogen source. Our results show that BAP2 expression is inducible by leucine in the poor nitrogen source proline, and that BAP2 expression is constitutive in the rich nitrogen source ammonium, with high values unaltered by the addition of leucine. We also demonstrate here that an active SPS pathway is necessary for BAP2 expression in both nitrogen conditions and in the presence or absence of the inducer leucine. Transcription factors Leu3, Gcn4 and Dal81 are also involved in BAP2 regulation in both a direct and an indirect way depending on the quality of the nitrogen source. We further demonstrate here that a physical interaction occurs between the transcription factor Uga3 and the regulatory region of the BAP2 gene, which leads to a strong positive regulation. We thus conclude that the transcription factors involved in BAP2 regulation affect its expression to different extents depending on the quality of the nitrogen source. We also demonstrate for the first time that Uga3, until now known as a transcriptional activator responsible for the induction of gamma-aminobutyric acid (GABA) genes, is one of the main positive regulators of BAP2 transcription. So we found that BAP2, a gene expressed under environmental conditions quite different from those of UGA expression, is also regulated by Dal81, Uga3 and Leu3 factors together with Gcn4 and Stp1/2.