NOVEL REGULATORY FACTORS INTERACTING WITH THE PROMOTER OF THE GENE ENCODING THE MESSENGER-RNA CAP-BINDING PROTEIN (EIF4E) AND THEIR FUNCTION IN GROWTH-REGULATION

Regulation of the mRNA cap binding protein (eIF4E) is critical to the control of cellular proliferation since this protein is the rate-limit ing factor in translation initiation and transforms fibroblasts and si nce eIF4E mutants arrest budding yeast in the G(1) phase of the cell c ycle (cdc33). We previously demonstrated regulation of eIF4E by altere d transcription of its mRNA in serum-stimulated fibroblasts and in res ponse to c-myc. To identify additional factors regulating eIF4E transc ription, we used linker-scanning constructs to characterize sites in t he promoter of the eIF4E gene required for its expression. Promoter ac tivity was dependent on sites at -5, -25, -45, and -75; the site at -7 5 included a previously described myc box. Electrophoretic mobility sh ift assays identified DNA-protein interactions at -25 and revealed a b inding site (TTACCCCCCCTT) that is unique to the eIF4E promoter. Prote ins of 68 and 97 kDa bound this site in UV cross-linking and Southwest ern experiments. Levels of 4E regulatory factor activities correlated with c-Myc levels, eIF4E expression levels, and protein synthesis in d ifferentiating U937 and HL60 cells, suggesting that these activities m ay function to regulate protein synthesis rates during differentiation . Since the eIF4E promoter lacked typical TATA and initiator elements, further studies of this novel initiator-homologous element should pro vide insights into mechanisms of transcription initiation and growth r egulation.