Fig. 1. Phosphorylation of specific sites in eIF4GI is modulated by serum. ³²P–labeled eIF4GI immunoprecipitated from 293 cells starved of serum for 36 h (–Serum or –S), or starved of serum for 36 h then stimulated with serum for 30 min (+Serum or +S), was subjected to (A) SDS–8% PAGE, then (B and C) to two-dimensional tryptic peptide mapping. The directions of chromatography (vertical) and electrophoresis (horizontal) as well as the loading origin (arrow) are indicated. Major phosphopeptides are numbered.