NOVEL FUNCTION OF THE TRANSCRIPTION FACTOR UGA3 AS AN ACTIVATOR OF BRANCHEDCHAIN AMINO ACID PERMEASE BAP2 GENE EXPRESSION

MUÑOZ SEBASTIAN ANIBAL; CORREA-GARCÍA, SUSANA; VALENCIA-GUILLEN JENNIFFER; GULIAS JUAN FACUNDO; BERMÚDEZ-MORETTI, MARIANA

Salta

Congreso; LV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2019

SAIB

Transcription regulation of most genes in yeast occurs at the level of activation, i.e. the basal level of expression is very low and increasedtranscription requires gene-specific transcription factors allowing the recruitment of basal transcriptional machinery. SaccharomycescerevisiaeBAP2gene encodes the permease responsible for the major part of leucine, valine and isoleucine uptake, amino acids that this yeast canuse as nitrogen sources. Moreover, BAP2 expression is known to be induced by the presence of amino acids such as leucine. However,BAP2regulation by nitrogen source quality has rendered controversial results and remains unclear.In this context, we analyzed the transcriptionalregulation of BAP2 in response to extracellular leucine in the presence of both a poor and a rich nitrogen source. Our results show that BAP2expression is inducible by leucine in the poor nitrogen source proline, and that BAP2 expression is constitutive in the rich nitrogen sourceammonium, with high values unaltered by the addition of leucine. We also demonstrate here that an active SPS pathway is necessary for BAP2expression in both nitrogen conditions and in the presence or absence of the inducer leucine. Transcription factors Leu3, Gcn4 and Dal81are alsoinvolved in BAP2 regulation in both a direct and an indirect way depending on the quality of the nitrogen source. We further demonstrate herethat a physical interaction occurs between the transcription factorUga3and the regulatory region of the BAP2 gene, which leads to a strongpositive regulation. We thus conclude that the transcription factors involved in BAP2 regulation affect its expression to different extentsdepending on the quality of the nitrogen source. We also demonstrate for the first time that Uga3, until now known as a transcriptional activatorresponsible for the induction of gamma-aminobutyric acid (GABA) genes, is one of the main positive regulators of BAP2 transcription. So wefound thatBAP2, 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.