eIF4G Dramatically Enhances the Binding of eIF4E to the mRNA 5′-Cap Structure*
- From the Department of Biochemistry and McGill Cancer Center, Faculty of Medicine, McGill University, Montreal, Quebec, Canada H3G 1Y6
Abstract
The cap structure, m7GpppN, is present at the 5′-end of all eukaryotic cellular (except organellar) mRNAs. Initiation of translation is mediated by the multisubunit initiation factor eIF4F, which binds the cap structure via its eIF4E subunit and facilitates the binding of mRNA to ribosomes. Here, we used recombinant proteins to reconstitute the cap recognition activity of eIF4F in vitro. We demonstrate that the interaction of eIF4E with the mRNA 5′-cap structure is dramatically enhanced by eIF4G, as determined by a UV-induced cross-linking assay. Furthermore, 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 another initiation factor, eIF4B, to the cap structure. In addition, the stimulatory effect of eIF4G on the cap recognition of eIF4E is inhibited by the translational repressor, 4E-BP1. These results suggest that eIF4E initially interacts with the mRNA cap structure as part of the eIF4F complex.
Footnotes
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↵* This work was supported by a grant from the Medical Research Council of Canada (to N. S.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Recipient of a Medical Research Council Distinguished Scientist Award from the Medical Research Council of Canada and is a Howard Hughes International Scholar. To whom correspondence should be addressed: Dept. of Biochemistry and McGill Cancer Center, Faculty of Medicine, McGill University, Montreal, Quebec, Canada H3G 1Y6. Tel.: 514-398-7274; Fax: 514-398-1287; E-mail:sonenberg{at}medcor.mcgill.ca.
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↵1 H. Lee, unpublished data.
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↵2 The abbreviation used is: GST, glutathioneS-transferase.
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↵3 H. Lee and C. Goyer, unpublished data.
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- Received April 9, 1997.
- Revision received May 30, 1997.
