Amino acid response

Amino acid response is the mechanism triggered in mammalian cells by amino acid starvation.
The amino acid response pathway is triggered by shortage of any essential amino acid, and results in an increase in activating transcription factor ATF4, which in turn affects many processes by sundry pathways to limit or increase the production of other proteins.
At low concentration of amino acid, GCN2 is activated due to the increase level of uncharged tRNA molecules. Activated GCN2 phosphorylates itself and elF2ɑ, it triggers a transcriptional and translational response to restore amino acid homeostasis by affecting the utilization, acquisition, and mobilization of amino acid in an organism. Essential amino acids are crucial to maintain homeostasis within an organism. Diet plays an important role in the health of an organism, as evidence ranging from human epidemiological to model organism experimental data suggests that diet-dependent pathways impact a variety of adult stem cells.
Leucine starvation.
PCAF is recruited specifically to the CHOP amino acid response element to enhance the ATF4 transcriptional activity.