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Molecular and Cellular Biology, March 2009, p. 1661-1669, Vol. 29, No. 6
0270-7306/09/$08.00+0     doi:10.1128/MCB.01187-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Requirement of RNA Binding of Mammalian Eukaryotic Translation Initiation Factor 4GI (eIF4GI) for Efficient Interaction of eIF4E with the mRNA Cap{triangledown} ,{dagger}

Akiko Yanagiya,1 Yuri V. Svitkin,1 Shoichiro Shibata,2 Satoshi Mikami,2 Hiroaki Imataka,2 and Nahum Sonenberg1*

Department of Biochemistry and McGill Cancer Center, McGill University, Montreal, Quebec, Canada H3G 1Y6,1 RIKEN Systems and Structural Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan2

Received 28 July 2008/ Returned for modification 29 August 2008/ Accepted 19 December 2008

Eukaryotic mRNAs possess a 5'-terminal cap structure (cap), m7GpppN, which facilitates ribosome binding. The cap is bound by eukaryotic translation initiation factor 4F (eIF4F), which is composed of eIF4E, eIF4G, and eIF4A. eIF4E is the cap-binding subunit, eIF4A is an RNA helicase, and eIF4G is a scaffolding protein that bridges between the mRNA and ribosome. eIF4G contains an RNA-binding domain, which was suggested to stimulate eIF4E interaction with the cap in mammals. In Saccharomyces cerevisiae, however, such an effect was not observed. Here, we used recombinant proteins to reconstitute the cap binding of the mammalian eIF4E-eIF4GI complex to investigate the importance of the RNA-binding region of eIF4GI for cap interaction with eIF4E. We demonstrate that chemical cross-linking of eIF4E to the cap structure is dramatically enhanced by eIF4GI fragments possessing RNA-binding activity. Furthermore, the fusion of RNA recognition motif 1 (RRM1) of the La autoantigen to the N terminus of eIF4GI confers enhanced association between the cap structure and eIF4E. These results demonstrate that eIF4GI serves to anchor eIF4E to the mRNA and enhance its interaction with the cap structure.

* Corresponding author. Mailing address: Department of Biochemistry, McGill University, McIntyre Medical Sciences Building, Rm. 807, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6. Phone: (514) 398-7274. Fax: (514) 398-1287. E-mail: nahum.sonenberg{at}mcgill.ca

{triangledown} Published ahead of print on 29 December 2008.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

Molecular and Cellular Biology, March 2009, p. 1661-1669, Vol. 29, No. 6
0270-7306/09/$08.00+0     doi:10.1128/MCB.01187-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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