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Nucleic Acids Research 2006 34(9):2495-2507; doi:10.1093/nar/gkl290
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Published online 10 May 2006

© The Author 2006. 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@oxfordjournals.org

Article

The two eIF4A helicases in Trypanosoma brucei are functionally distinct

Rafael Dhalia, Nina Marinsek1, Christian R. S. Reis, Rodolfo Katz, João R. C. Muniz2, Nancy Standart1, Mark Carrington1 and Osvaldo P. de Melo Neto*

Centro de Pesquisas Aggeu Magalhães, Fundação Oswaldo Cruz Avenue Moraes Rego s/n, Campus UFPE, Recife PE 50670-420, Brazil 1 Department of Biochemistry, University of Cambridge 80 Tennis Court Road, Cambridge CB2 1GA, UK 2 Instituto de Física de São Carlos, Universidade de São Paulo Caixa Postal 369, São Carlos SP 13560-970, Brazil

*To whom correspondence should be addressed. Tel: 55 81 2101 2636; Fax: 55 81 3453 2449; Email: opmn{at}cpqam.fiocruz.br

Received February 1, 2006. Revised March 4, 2006. Accepted April 6, 2006.

Protozoan parasites belonging to the family Trypanosomatidae are characterized by an unusual pathway for the production of mRNAs via polycistronic transcription and trans-splicing of a 5' capped mini-exon which is linked to the 3' cleavage and polyadenylation of the upstream transcript. However, little is known of the mechanism of protein synthesis in these organisms, despite their importance as agents of a number of human diseases. Here we have investigated the role of two Trypanosoma brucei homologues of the translation initiation factor eIF4A (in the light of subsequent experiments these were named as TbEIF4AI and TbEIF4AIII). eIF4A, a DEAD-box RNA helicase, is a subunit of the translation initiation complex eIF4F which binds to the cap structure of eukaryotic mRNA and recruits the small ribosomal subunit. TbEIF4AI is a very abundant predominantly cytoplasmic protein (over 1 x 105 molecules/cell) and depletion to ~10% of normal levels through RNA interference dramatically reduces protein synthesis one cell cycle following double-stranded RNA induction and stops cell proliferation. In contrast, TbEIF4AIII is a nuclear, moderately expressed protein (~1–2 x 104 molecules/cell), and its depletion stops cellular proliferation after approximately four cell cycles. Ectopic expression of a dominant negative mutant of TbEIF4AI, but not of TbEIF4AIII, induced a slow growth phenotype in transfected cells. Overall, our results suggest that only TbEIF4AI is involved in protein synthesis while the properties and sequence of TbEIF4AIII indicate that it may be the orthologue of eIF4AIII, a component of the exon junction complex in mammalian cells.


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