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Nucleic Acids Research Advance Access originally published online on December 1, 2007
Nucleic Acids Research 2008 36(2):589-597; doi:10.1093/nar/gkm1072
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Nucleic Acids Research, 2008, Vol. 36, No. 2 589-597
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Molecular Biology

The interaction of mammalian mitochondrial translational initiation factor 3 with ribosomes: evolution of terminal extensions in IF3mt

Md. Emdadul Haque, Domenick Grasso 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: +1 919 843 1580; Email: linda_spremulli{at}unc.edu

Received October 11, 2007. Revised November 13, 2007. Accepted November 13, 2007.

Mammalian mitochondrial initiation factor 3 (IF3mt) has a central region with homology to bacterial IF3. This homology region is preceded by an N-terminal extension and followed by a C-terminal extension. The role of these extensions on the binding of IF3mt to mitochondrial small ribosomal subunits (28S) was studied using derivatives in which the extensions had been deleted. The Kd for the binding of IF3mt to 28S subunits is ~30 nM. Removal of either the N- or C-terminal extension has almost no effect on this value. IF3mt has very weak interactions with the large subunit of the mitochondrial ribosome (39S) (Kd = 1.5 µM). However, deletion of the extensions results in derivatives with significant affinity for 39S subunits (Kd = 0.12–0.25 µM). IF3mt does not bind 55S monosomes, while the deletion derivative binds slightly to these particles. IF3mt is very effective in dissociating 55S ribosomes. Removal of the N-terminal extension has little effect on this activity. However, removal of the C-terminal extension leads to a complex dissociation pattern due to the high affinity of this derivative for 39S subunits. These data suggest that the extensions have evolved to ensure the proper dissociation of IF3mt from the 28S subunits upon 39S subunit joining.


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