Ribosomal Protein S1 Associates with Escherichia coli Ribosomal 30‐S Subunit by Means of Protein‐Protein Interactions

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Abstract
Ribosomal proteins S1 when associated with the 30-S subunit does not interact with 16-S RNA but is binding is determined mostly by protein-protein interactions. These conclusions are based on the following data. UV irradiation (.lambda. = 254 nm) of the 30-S subunit does not result in the covalent cross-linking of S1 with 16-S RNA at irradiation doses up to 150 quanta/nucleotide, whereas the irradiation under the same conditions of S1.cntdot.polynucleotide complexes [S1.cntdot.poly(U), S1.cntdot.poly(A) and S1.cntdot. phage RNA] induces effective formation of polynucleotide-protein cross-links. Mild treatment of 30-S subunits lacking S-1 with RNase A or with cobra venom endonuclease results in removal of 10-20% of the total nucleotide material but does not affect their sedimentation characteristics or their S1 binding capacity. The association of S1 with S1-depleted 30-S subunits is insensitive to aurintricarboxylic acid, which is known as a strong inhibitor of complex formation between S1 and polynucleotides. Mild trypsin treatment of S1-depleted 30-S subunits greatly reduces their S1 binding capacity.