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Mol. Cell. Biol., 01 1998, 334-342, Vol 18, No. 1
A Gradi, H Imataka, YV Svitkin, E Rom, B Raught, S Morino and N Sonenberg
Mammalian eukaryotic translation initiation factor 4F (eIF4F) is a cap-
binding protein complex consisting of three subunits: eIF4E, eIF4A, and
eIF4G. In yeast and plants, two related eIF4G species are encoded by two
different genes. To date, however, only one functional eIF4G polypeptide,
referred to here as eIF4GI, has been identified in mammals. Here we
describe the discovery and functional characterization of a closely related
homolog, referred to as eIF4GII. eIF4GI and eIF4GII share 46% identity at
the amino acid level and possess an overall similarity of 56%. The homology
is particularly high in certain regions of the central and carboxy
portions, while the amino-terminal regions are more divergent. Far-Western
analysis and coimmunoprecipitation experiments were used to demonstrate
that eIF4GII directly interacts with eIF4E, eIF4A, and eIF3. eIF4GII, like
eIF4GI, is also cleaved upon picornavirus infection. eIF4GII restores cap-
dependent translation in a reticulocyte lysate which had been pretreated
with rhinovirus 2A to cleave endogenous eIF4G. Finally, eIF4GII exists as a
complex with eIF4E in HeLa cells, because eIF4GII and eIF4E can be purified
together by cap affinity chromatography. Taken together, our findings
indicate that eIF4GII is a functional homolog of eIF4GI. These results may
have important implications for the understanding of the mechanism of
shutoff of host protein synthesis following picornavirus infection.
Copyright © 1998, American Society for Microbiology
A novel functional human eukaryotic translation initiation factor 4G
Department of Biochemistry and McGill Cancer Center, McGill University, Montreal, Quebec, Canada.
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