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Báo cáo khoa học: Characterization of eIF3k A newly discovered subunit of mammalian translation initiation factor eIF3

Mammalian translation initiation factor 3 (eIF3) is a multisubunit complex containingat least 12 subunitswithan apparent aggregate mass of 700 kDa.eIF3 binds to the 40S ribosomal subunit, promotes the binding of methionyl-tRNA i and mRNA, and interacts with several other initi-ation factors to form the 40S initiation complex.Human cDNAs encoding 11 of the 12 subunits have been isolated previously; here we report the cloning and characterization of a twelfth subunit, a 28-kDa protein named eIF3k.Evi-dence that eIF3k is present in the eIF3 complex was obtained | Eur. J. Biochem. 270 4133-4139 2003 FEBS 2003 doi 10.1046 j.1432-1033.2003.03807.x Characterization of eIF3k A newly discovered subunit of mammalian translation initiation factor eIF3 Greg L. Mayeur Christopher S. Fraser Franck Peiretti Karen L. Block and John W. B. Hershey Department of Biological Chemistry School of Medicine University of California Davis CA USA Mammalian translation initiation factor 3 eIF3 is a multisubunit complex containing at least 12 subunits with an apparent aggregate mass of w 700 kDa. iIF3 hinds to the 40S ribosomal subunit promotes the binding of methionyl-tRNAi and mRNA and interacts with several other initiation factors to form the 40S initiation complex. Human cDNAs encoding 11 of the 12 subunits have been isolated previously here we report the cloning and characterization of a twelfth subunit a 28-kDa protein named eIF3k. I id-dence that eIF3k is present in the eIF3 complex was obtained. A monoclonal nni i-iF33a pl70 Ig coimmunoprecipitates eIF3k with the eIF3 complex. Affinity purification of histidine-tagged eIF3k from transiently transfected COS cells copurifies other eIF3 subunits. eIF3k colocalizes with eIF3 on 40S ribosomal subunits. eIF3k c -expres-ed with five other core eIF3 subunits in baculovirus-infected insect cells forms a stable immunoprecipitatable complex with the core . IlFkk mte3naSs directly wtth iIFcc IlFgg and eIF3j by glutathione S-transferase pull-down assays. Sequences homologous with eIF3k are found in the genomes of Caenorhabitis elegans Arabidopsis thaliana and Drosophila melanogaster and a homologous protein has been reported to be present in wheat eIF3. Rs ubu Liilous expression in human tissues yet its apparent absence in Saccharomyces cerevisiae and Schizosaccharomyces pombe suggest a unique regulatory role for eIF3k in higher organisms. The tUudies mf eIF3k compfete the chai actei i ahon of mammalian eIF3 subunits. Keywords protein synthesis translation initiation initiation factor eIF3 eIF3k. .