Immunochemical detection of proteins in the small subunit of rat liver ribosomes involved in binding of the ternary initiation complex

Abstract

An essential step of peptide chain initiation in eukaryotes is the binding of the ternary initiation complex [Met-tRNAfX eIF-2 X GTP] to the P site of small ribosomal subunit, thus forming the quaternary initiation complex [40 S subunit X Met-tRNA,X eIF-2 X GTP] [ l-41. First attempts to analyze proteins of the small subunit of rat liver ribosomes involved in binding of components of the ternary initiation complex have been made by the application of antibodies [5] and by crosslinking experiments [6]. In [S] we described the effect of antibodies against ribosomal protein S3 (according to the newly proposed common nomenclature of eukaryotic ribosomal proteins [7]) on the binding of [3H]Met-tRNAfin complex with eIF-2 and GTP to the 40 S ribosomal subunit. We now report further experiments with antibodies against 9 proteins of the small ribosomal subunit. From the strong inhibitory activity of the antibodies against ribosomal proteins S3, S6, and S13 and their location on the small ribosomal subunit as studied by immune electron microscopy ([8,9] and unpublished) it is concluded that these proteins are involved in the P site organization and that the P site is located in the head region of the small ribosomal subunit.