Structural Roles for Human Translation Factor eIF3 in Initiation of Protein Synthesis

doi:10.1126/science.1118977

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Science 2 December 2005:
Vol. 310. no. 5753, pp. 1513 - 1515
DOI: 10.1126/science.1118977

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Structural Roles for Human Translation Factor eIF3 in Initiation of Protein Synthesis

Bunpote Siridechadilok,¹ Christopher S. Fraser,¹^,3^* Richard J. Hall,⁴^* Jennifer A. Doudna,¹^,2^,3^,4 Eva Nogales¹^,3^,4

Protein synthesis in mammalian cells requires initiation factoreIF3, a $~$ 750-kilodalton complex that controls assembly of 40Sribosomal subunits on messenger RNAs (mRNAs) bearing eithera 5'-cap or an internal ribosome entry site (IRES). Cryo–electronmicroscopy reconstructions show that eIF3, a five-lobed particle,interacts with the hepatitis C virus (HCV) IRES RNA and the5'-cap binding complex eIF4F via the same domain. Detailed modelingof eIF3 and eIF4F onto the 40S ribosomal subunit reveals thateIF3 uses eIF4F or the HCV IRES in structurally similar waysto position the mRNA strand near the exit site of 40S, promotinginitiation complex assembly.

¹ Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
² Department of Chemistry, University of California, Berkeley, CA 94720, USA.
³ Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.
⁴ Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

^* These authors contributed equally to this work.

To whom correspondence should be addressed. E-mail: enogales{at}lbl.gov (E.N.); doudna{at}berkeley.edu (J.A.D.)