RAS2/PKA pathway activity is involved in the nitrogen regulation of l-leucine uptake in Saccharomyces cerevisiae

• Published in: The international journal of biochemistry & cell biology 1997-03, Vol.29 (3), p.505-512
• Main Authors: Sáenz, Daniel A., Chianelli, Mónica S., Stella, Carlos A., Mattoon, James R., Ramos, Eugenia H.
• Format: Article
• Language: English
• Subjects: Amino Acid Transport Systems; Amino Acids - analysis; Amino Acids - metabolism; Biological Transport; Culture Media; Cyclic AMP-Dependent Protein Kinases - metabolism; Fungal Proteins - genetics; Fungal Proteins - metabolism; Genes, Dominant; Kinetics; l-Leucine transport; Leucine - metabolism; Leucine - pharmacokinetics; Membrane Transport Proteins - metabolism; Mutation; Nitrogen - metabolism; Nitrogen regulation; Proline - metabolism; Proline - pharmacology; ras Proteins - genetics; ras Proteins - metabolism; RAS2 gene; RAS2/PKA pathway; Saccharomyces cerevisiae; Saccharomyces cerevisiae - drug effects; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/S1357-2725(96)00102-1

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 RAS2 val19 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 NH 4 + 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 K T values are of the same order as those of S1 and S2 l-leucine permeases. Mutation in the RAS2 gene alters initial velocities and J max values in both high and low affinity l-leucine transport systems. Activation of the RAS2/PKA signalling pathway by the RAS2 val19 mutation, blocks the response to a poor nitrogen source whereas inactivation of RAS2 by gene disruption, results in an increase of the same response.