Practice question

Phosphorylation of eIF2 alpha at Ser51 sequesters eIF2B pentameric guanine nucleotide exchange factor that normally regenerates active ternary complex eIF2 GTP Met-tRNAi from inactive GDP form. Since cellular eIF2B concentration is about tenfold lower than eIF2, even modest phosphorylation proportion immobilizes most eIF2B, collapsing ternary complex availability. Consequently global cap-dependent translation is rapidly shut down, conserving energy and reducing endoplasmic reticulum client load, while messenger RNAs containing upstream open reading frames such as ATF4 and CHOP escape repression via delayed reinitiation, orchestrating adaptive stress transcriptome.