EIF4G DRAMATICALLY ENHANCES THE BINDING OF EIF4E TO THE MESSENGER-RNA5'-CAP STRUCTURE

The cap structure, m(7)GpppN, is present at the 5'-end of all eukaryot ic cellular (except organellar) mRNAs, Initiation of translation is me diated by the multisubunit initiation factor eIF4F, which binds the ca p structure via its eIF4E subunit and facilitates the binding of mRNA to ribosomes, Here, we used recombinant proteins to reconstitute the c ap recognition activity of eIF4F in vitro, We demonstrate that the int eraction of eIF4E with the mRNA 5'-cap structure is dramatically enhan ced by eIF4G, as determined by a UV-induced cross-linking assay, Furth ermore, assembly of the eIF4F complex at the cap structure, as well as ATP hydrolysis, is shown to be a requisite for the cross-linking of a nother initiation factor, eIF4B, to the cap structure, In addition, th e stimulatory effect of eIF4G on the cap recognition of eIF4E is inhib ited by the translational repressor, 4E-BP1, These results suggest tha t eIF4E initially interacts with the mRNA cap structure as part of the eIF4F complex.