Abstract
Platelet‐derived growth factor exerts rapid effects on protein synthesis and polysome formation in cultured cells. We report that platelet‐derived growth factor stimulates a rapid phosphorylation of eIF‐4E in WI‐38 human lung fibroblasts. The effect was dependent on both time and PDGF concentrations. Phosphoserine was the sole phosphoamino acid identified and tryptic phosphopeptide maps showed a single phosphopeptide under both control and PDGF conditions. Phosphorylation of eIF‐4E may be one of the events required for initiating entry into G1 and commitment into S phase of the cell cycle.