CHARACTERIZATION OF CDNAS ENCODING THE P44 AND P35 SUBUNITS OF HUMAN TRANSLATION INITIATION-FACTOR EIF3

Eukaryotic translation initiation factor 3 (eIF3) is a large multisubu nit complex that plays a central role in the initiation of translation . It binds to 40 S ribosomal subunits resulting in dissociation of 80 S ribosomes, stabilizes initiator methionyl-tRNA binding to 40 S subun its, and is required for mRNA binding. eIF3 has an aggregate molecular mass of similar to 600 kDa and comprises at least 10 subunits, The cD NAs encoding eight of the subunits have been cloned previously (p170, pile, p110, p66, p48, p47, p40, and p36), Here we report the cloning a nd characterization of human cDNAs encoding two more subunits of human eIF3, namely eIF3-p44 and eIF3-p35. These proteins are immunoprecipit ated by affinity-purified anti-eIF3-p170 antibodies, indicating they a re components of the eIF3 complex. Far Western analysis shows that eIF 3-p44 interacts strongly and specifically with the eIF3-p170 subunit, and weakly with p116/p110, p66, p40, and itself. eIF3-p44 contains an RNA recognition motif near its C terminus. Northwestern blotting shows that eIF3-p44 binds 18 S rRNA and beta-globin mRNA. Possession of clo ned cDNAs encoding all 10 subunits of eIF3 provides the tools necessar y to elucidate the functions of the individual subunits and the struct ure of the eIF3 complex.