THE PHOSPHORYLATION STATE OF TRANSLATION INITIATION-FACTORS IS REGULATED DEVELOPMENTALLY AND FOLLOWING HEAT-SHOCK IN WHEAT

Several translation initiation factors in mammals and yeast are regula ted by phosphorylation. The phosphorylation state of these factors is subject to alteration during development, environmental stress (heat s hock, starvation, or heme deprivation), or viral infection. The phosph orylation state and the effect of changes in phosphorylation of the tr anslation initiation factors of higher plants have not been previously investigated, We have determined the isoelectric states for the wheat translation initiation factors eIF-4A, eIF-4B, eIF-4F, eIF-iso4F, and eIF-2 and the poly(A)-binding protein in the seed, during germination , and following heat shock of wheat seedlings using two-dimensional ge l electrophoresis and Western analysis. We found that the developmenta lly induced changes in isoelectric state observed during germination o r the stress-induced changes were consistent with changes in phosphory lation. Treatment of the phosphorylated forms of the factors with phos phatases confirmed that the nature of the modification was due to phos phorylation. The isoelectric states of eIF-4B, eIF-4F (eIF-4E, p26), e IF-iso4F (eIF-iso4E, p28), and eIF-2 alpha (p42) were altered during g ermination, suggesting that phosphorylation of these factors is develo pmentally regulated and correlates with the resumption of protein synt hesis that occurs during germination. The phosphorylation of eIF-2 bet a (p38) or poly(A)-binding protein did not change either during germin ation or following a thermal stress. Only the phosphorylation state of two factors, eIF-4A and eIF-4B, changed following a heat shock, sugge sting that plants may differ significantly from animals in the way in which their translational machinery is modified in response to a therm al stress.