Structure of cDNAs Encoding Human Eukaryotic Initiation Factor 3 Subunits

Abstract

The mammalian translation initiation factor 3 (eIF3), is a multiprotein complex of 600 kDa that binds to the 40 S ribosome and promotes the binding of methionyl-tRNA i and mRNA. cDNAs encoding 5 of the 10 subunits, namely eIF3-p170,-p116,-p110,-p48, and-p36, have been isolated previously. Here we report the cloning and characterization of human cDNAs encoding the major RNA binding subunit, eIF3-p66, and two additional sub-units, eIF3-p47 and eIF3-p40. Each of these proteins is present in immunoprecipitates formed with affinity-purified anti-eIF3-p170 antibodies. Human eIF3-p66 shares 64% sequence identity with a hypothetical Caenorhab-ditis elegans protein, presumably the p66 homolog. Deletion analyses of recombinant derivatives of eIF3-p66 show that the RNA-binding domain lies within an N-terminal 71-amino acid region rich in lysine and argi-nine. The N-terminal regions of human eIF3-p40 and eIF3-p47 are related to each other and to 17 other eu-karyotic proteins, including murine Mov-34, a subunit of the 26 S proteasome. Phylogenetic analyses of the 19 related protein sequences, called the Mov-34 family, distinguish five major subgroups, where eIF3-p40, eIF3-p47, and Mov-34 are each found in a different subgroup. The subunit composition of eIF3 appears to be highly conserved in Drosophila melanogaster, C. elegans, and Arabidopsis thaliana, whereas only 5 homologs of the 10 subunits of mammalian eIF3 are encoded in S. cerevisiae.