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Nucleic Acids Research 2005 33(22):7011-7018; doi:10.1093/nar/gki1007
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Published online 9 December 2005

© The Author 2005. Published by Oxford University Press. All rights reserved
The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact journals.permissions{at}oxfordjournals.org

Article

Role of the N- and C-terminal extensions on the activity of mammalian mitochondrial translational initiation factor 3

Kalpana Bhargava and Linda L. Spremulli*

Department of Chemistry, University of North Carolina at Chapel Hill Chapel Hill, NC 27599-3290, USA

*To whom correspondence should be addressed. Tel: +1 919 966 1567; Fax: +1 919 966 3675; Email: Linda_Spremulli{at}unc.edu

Received October 21, 2005. Revised November 22, 2005. Accepted November 22, 2005.

Mammalian mitochondrial translational initiation factor 3 (IF3mt) promotes initiation complex formation on mitochondrial 55S ribosomes in the presence of IF2mt, fMet-tRNA and poly(A,U,G). The mature form of IF3mt is predicted to be 247 residues. Alignment of IF3mt with bacterial IF3 indicates that it has a central region with 20–30% identity to the bacterial factors. Both the N- and C-termini of IF3mt have extensions of ~30 residues compared with bacterial IF3. To examine the role of the extensions on IF3mt, deletion constructs were prepared in which the N-terminal extension, the C-terminal extension or both extensions were deleted. These truncated derivatives were slightly more active in promoting initiation complex formation than the mature form of IF3mt. Mitochondrial 28S subunits have the ability to bind fMet-tRNA in the absence of mRNA. IF3mt promotes the dissociation of the fMet-tRNA bound in the absence of mRNA. This activity of IF3mt requires the C-terminal extension of this factor. Mitochondrial 28S subunits also bind mRNA independently of fMet-tRNA or added initiation factors. IF3mt has no effect on the formation of these complexes and cannot dissociate them once formed. These observations have lead to a new model for the function of IF3mt in mitochondrial translational initiation.

Present address: Kalpana Bhargava, Department of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri, Kansas City, MO 64110, USA


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