We have found that E. coli ribosomal protein S13 recognizes multiple sites on 16S RNA. However, when protein S19 is included with a mixture of proteins S4, S7, S8, S16/S17 and S20, the S13 binds to the complex with measurably greater strength and with a stolchlometry of 1.5 copies per particle. This suggests that the protein may have two functional domains. Wehave tested this idea by cleaving the protein into two polypeptides. It was found that one of the fragments, composed of amino acid residues 84-117, retained the capacity to bind 16S RNA at multiple sites. Protein S19 had no affect on the strength or stoichlometry of the binding of this fragment. These data suggest that S13 has a C-terminal domain primarily responsible for RNA recognition and possibly that the N-termlnal region is important for association with protein S19.
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