EXPRESSION OF A PHOSPHORYLATION-RESISTANT EUKARYOTIC INITIATION FACTOR-II ALPHA-SUBUNIT MITIGATES HEAT-SHOCK INHIBITION OF PROTEIN-SYNTHESIS

Protein synthesis is dramatically reduced upon exposure of cells to el evated temperature. Concordant with this inhibition, multiple phosphor ylation and dephosphorylation reactions occur on specific eukaryotic i nitiation factors that are required for protein synthesis. Most notabl y, phosphorylation of the alpha-subunit of eukaryotic initiation facto r-2 (eIF-2alpha) on serine residue 51 occurs. To identify the importan ce of phosphorylation in control of protein synthesis, we have evaluat ed the effects of expression of a mutant eIF-2alpha which is resistant to phosphorylation. Expression of a serine to alanine mutant at resid ue 51 of eIF-2alpha partially protected cells from the inhibition of p rotein synthesis in response to heat treatment. The overexpressed seri ne to alanine 51 mutant subunit was incorporated into the eIF-2 hetero trimer and was resistant to phosphorylation. These results are consist ent with the hypothesis that heat shock inhibition of translation is m ediated in part through phosphorylation of eIF-2alpha. Expression of t he wild type or mutant eIF-2alpha did not affect cell survival or indu ction of hsp70 mRNA upon heat shock, indicating that although eIF-2alp ha is a heat shock-induced protein, its increased synthesis during hea t shock does not alter the heat-shock response.