Integration of general amino acid control and target of rapamycin (TOR) regulatory pathways in nitrogen assimilation in yeast.
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 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 found that GAAC is a major effector of the TOR pathway, with Gcn4p and Gln3p each inducing a similar number of genes during rapamycin treatment. Although 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 the assimilation of secondary nitrogen sources such as gamma-aminobutyric acid (GABA). Gcn2p activation upon shifting to secondary nitrogen sources is suggested to occur by means of a dual mechanism. First, Gcn2p is induced by the release of TOR repression through a mechanism involving Sit4p protein phosphatase. Second, this eIF2 kinase is activated by select uncharged tRNAs, which were shown to accumulate during the shift to the 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.
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Kirk A
KA
Staschke
Souvik
S
Dey
John M
JM
Zaborske
Lakshmi Reddy
LR
Palam
Jeanette N
JN
McClintick
Tao
T
Pan
Howard J
HJ
Edenberg
Ronald C
RC
Wek
D000596:Amino Acids / Q000737:chemistry*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D008954:Models, Biological; D009584:Nitrogen / Q000737:chemistry*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D054648:Protein Phosphatase 2 / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D012343:RNA, Transfer / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013045:Species Specificity; D058570:TOR Serine-Threonine Kinases; D014158:Transcription, Genetic; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000596:Amino Acids; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; D005680:gamma-Aminobutyric Acid; D012343:RNA, Transfer; C512912:GCN2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D054648:Protein Phosphatase 2; C104343:SIT4 protein, S cerevisiae; D009584:Nitrogen