Mutation at the acidic residue-rich domain of eukaryotic initiation factor 2 (eIF2α)-associated glycoprotein p67 increases the protection of eIF2α phosphorylation during heat shock

Eukaryotic initiation factor 2 (eIF2)-associated glycoprotein p67 protects eIF2α phosphorylation from kinases. The N-terminal lysine-rich domains increase this activity and the acidic residue-rich domain inhibits it. Conserved amino acid residues D251, D262, E364, and E459 are involved in this inhibition. During heat shock, the overall protein synthesis rate decreases due to the increased levels of eIF2α phosphorylation. In this study, we examined whether the above inhibition is also found during heat shock. Indeed, the acidic residue-rich domain mutant (D6/2) showed a decreased level of eIF2α phosphorylation, and its second-site alanine substitutions at D251, D262, and E459 reversed this effect, whereas second-site alanine substitution at H331 and E364 residues further augmented it. A high-molecular-weight phosphoprotein and at least two faster-migrating phosphoproteins were detected by the monospecific polyclonal antibody against eIF2α(P) form in rat tumor hepatoma cells constitutively expressing the double mutant D6/2 + D251A. Although the levels of p67 mutants were unaffected during heat shock, those of p67 and p67-deactivating enzyme varied. Furthermore, the overall rate of protein synthesis correlated with the level of eIF2α phosphorylation. Taken together, these results suggest that the lysine-rich domains and conserved amino acid residues of p67 are involved in the regulation of eIF2α phosphorylation during heat shock.