The regulation of initiation of protein synthesis by phosphorylation of eIF-2(alpha) and the role of reversing factor in the recycling of eIF-2.

The capacity of whole reticulocyte lysates to catalyze the dissociation of exogenously added eIF-2 X [3H]GDP was determined as a measure of their reversing factor (RF) activity in the recycling of eIF-2 for the maintenance or restoration of protein synthesis. We have examined the relationship of RF activity to the protein synthetic activity of the lysate under normal conditions and on inhibition of protein synthesis by heme deficiency, double-stranded RNA, or oxidized glutathione. A direct correlation was found between a lysate's capacity to synthesize protein and its ability to stimulate the dissociation of eIF-2 X GDP. These findings further support the proposed mechanism by which the phosphorylation of only 30-40% of the eIF-2(alpha) in the lysate renders the limiting amount of RF present non-functional, impairing the recycling of eIF-2 and thereby inhibiting the initiation of protein synthesis.