Staschke KA, et al. (2010)
Integration of general amino acid control and target of rapamycin (TOR) regulatory pathways in nitrogen assimilation in yeast. J Biol Chem
Abstract: Two important nutrient sensing and regulatory pathways, the general amino acid control (GAAC) and the target of rapamycin (TOR), participate in the control of yeast growth and metabolism during changes in nutrient availability. Amino acid starvation activates the GAAC through Gcn2p phosphorylation of the translation factor eIF2 and preferential translation of GCN4, a transcription activator. TOR senses nitrogen availability and regulates transcription factors, such as Gln3p. We used microarray analyses to address the integration of the GAAC and TOR pathways in directing the yeast transcriptome during amino acid starvation and rapamycin treatment. We find that the GAAC is a major effector of the TOR pathway, with Gcn4p and Gln3p each inducing a similar number of genes during rapamycin treatment. While Gcn4p activates a common core of 57 genes, the GAAC directs significant variations in the transcriptome during different stresses. In addition to inducing amino acid biosynthetic genes, Gcn4p in conjunction with Gln3p activates genes required for assimilation of secondary nitrogen sources, such as gamma-amino-butyric acid (GABA). Gcn2p activation upon shifting to secondary nitrogen sources is suggested to occur by a dual mechanism. First, Gcn2p is induced by release of TOR repression through a mechanism involving Sit4p protein phosphatase. Second, this eIF2 kinase is activated by select uncharged tRNAs, which were shown accumulate during the shift to GABA medium. This study highlights the mechanisms by which the GAAC and TOR pathways are integrated to recognize changing nitrogen availability and direct the transcriptome for optimal growth adaptation.
||Type: Journal Article ||PubMed ID: 20233714 |