Identification of cDNA clones for the large subunit of eukaryotic translation initiation factor 3. Comparison of homologues from human, Nicotiana tabacum, Caenorhabditis elegans, and Saccharomyces cerevisiae

Initiation of translation in eukaryotes is mediated by a set of initiation factors. Mammalian initiation factor 3 is composed of at least 8 subunits, with the largest being about 180 kDa in size. Here we report the cloning of the p 180 subunit of human eukaryotic translation initiation factor (eIF) 3. The amine acid sequence deduced from the cDNA agrees with the sequences of CNBr fragments of eIF-3, confirming the identity of the clone. The 1382 amine acid open reading frame contains a high percentage of charged residues (48%) and an unusual repetitive domain near the carboxyl terminus composed of 25 repeats of 10 amine acids each. Data base searches identified related sequences found in members of the plant and fungal kingdoms as well as in other mammals and the nematode Caenorhabditis elegans. These sequences share significant identity with the human clone and probably represent the homologues of the p180 subunit in these organisms. This is the first report identifying the sequence of the large subunit of eIF-3.