title: RAS2/PKA pathway activity is involved in the nitrogen regulation of L-leucine uptake in Saccharomyces cerevisiae.
abstract: The aim of the present work is to study the participation of RAS2/PKA signal pathway in the nitrogen regulation of L-leucine transport in yeast cells. The study was performed on Saccharomyces cerevisiae isogenic strains with the normal RAS2 gene, the RAS2val19 mutant and the disrupted ras2::LEU2. These strains bring about different activities of the RAS2/PKA signal pathway, L-(14C)-Amino acid uptake measurements were determined in cells grown in a rich YPD medium with a mixed nitrogen source or in minimal media containing NH4+ or L-proline as the sole nitrogen source. We report herein that in all strains used, even in those grown in a minimal proline medium, the activity of the general amino acid permease (GAP1) was not detected. L-Leucine uptake in these strains is mediated by two kinetically characterized transport systems. Their KT values are of the same order as those of S1 and S2 L-leucine permeases. Mutation in the RAS2 gene alters initial velocities and Jmax values in both high and low affinity L-leucine transport systems. Activation of the RAS2/PKA signalling pathway by the RAS2val19 mutation, blocks the response to a poor nitrogen source whereas inactivation of RAS2 by gene disruption, results in an increase of the same response.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
authors.forename: D A
authors.initials: DA
authors.lastname: Sáenz
authors.forename: M S
authors.initials: MS
authors.lastname: Chianelli
authors.forename: C A
authors.initials: CA
authors.lastname: Stella
authors.forename: J R
authors.initials: JR
authors.lastname: Mattoon
authors.forename: E H
authors.initials: EH
authors.lastname: Ramos
mesh_terms: D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000032:analysis / Q000378:metabolism; D001692:Biological Transport; D003470:Culture Media; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005799:Genes, Dominant; D007700:Kinetics; D007930:Leucine / Q000378:metabolism / Q000493:pharmacokinetics*; D026901:Membrane Transport Proteins / Q000378:metabolism; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D011392:Proline / Q000378:metabolism / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D003470:Culture Media; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D011392:Proline; D017868:Cyclic AMP-Dependent Protein Kinases; C489015:RAS2 protein, S cerevisiae; D018631:ras Proteins; D007930:Leucine; D009584:Nitrogen