Characterization of eIF3k: a newly discovered subunit of mammalian translation initiation factor elF3

Eur J Biochem. 2003 Oct;270(20):4133-9. doi: 10.1046/j.1432-1033.2003.03807.x.

Abstract

Mammalian translation initiation factor 3 (eIF3) is a multisubunit complex containing at least 12 subunits with an apparent aggregate mass of approximately 700 kDa. eIF3 binds 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. Evidence that eIF3k is present in the eIF3 complex was obtained. A monoclonal anti-eIF3a (p170) 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 coexpressed with five other 'core' eIF3 subunits in baculovirus-infected insect cells, forms a stable, immunoprecipitatable, complex with the 'core'. eIF3k interacts directly with eIF3c, eIF3g 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. Its ubiquitous 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 studies of eIF3k complete the characterization of mammalian eIF3 subunits.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • DNA, Complementary / metabolism
  • Eukaryotic Initiation Factor-3 / genetics
  • Eukaryotic Initiation Factor-3 / isolation & purification
  • Eukaryotic Initiation Factor-3 / metabolism*
  • HeLa Cells
  • Humans
  • Protein Structure, Quaternary
  • Ribosomes

Substances

  • DNA, Complementary
  • Eukaryotic Initiation Factor-3