Specific interaction of one subunit of eukaryotic initiation factor eIF-3 with 18S ribosomal RNA within the binary complex, eIF-3.small ribosomal subunit, as shown by cross-linking experiments

Initiation factor eIF-3 from rat liver forms a binary complex with the small ribosomal subunit. Within this complex, 18S ribosomal RNA can be cross-linked to the 66 000 dalton subunit of eIF-3 by treating the complex with a short bifunctional reagent, diepoxybutane, with a distance of 4A between the reactive groups. In binary complexes containing eIF-3 premodified with the heterobifunctional reagent, methyl-p-azido-benzoylaminoacetimidate (10A), the 66 000 dalton subunit of eIF-3 became covalently bound to 18S rRNA after irradiation of the complex with ultraviolet light. The involvement of only one of the eight eIF-3 subunits in the formation of the covalent RNA-protein complexes indicates a highly specific interaction between 18S rRNA and eIF-3 at the attachment site of the factor on the 40S subunit.