The primary structure of ribosomal protein S7 from Escherichia coli strains K and B. Sequence of the C-terminal region of S7K and S7B.

Protein S7 from the small subunit of Escherichia coli ribosomes interacts specifically with the 16 S RNA (reviewed in reference [ 1 ] ) and it has been shown that binding occurs near the 3’-end of the 16 S RNA [2-41. Protein S7 can be cross-linked to 16 S RNA by ultraviolet irradiation of the small subunit [5]. From studies in which an in vitro complex between protein S7 and 16 S RNA was irradiated and digested with trypsin, it was suggested that four peptides were cross-linked to the RNA [6]. Knowledge of the primary structure of protein S7 is necessary both for detailed studies of the molecular mechanisms of protein-RNA interaction as well as the elucidation of the alterations of protein S7 recently found in various mutants of E. coli [7,8]. It has long been known that E. coli strains differ in their S7 proteins [9-131. Ribosomes from strains B, C and MRE 600 contain a protein S7 which differs extensively in size, charge, amino acid composition and immunological properties from the protein S7 in strain K [ 131 . In this paper, we describe the sequence analysis of the C-terminal regions of proteins. S7 isolated from E. coli strains B and K. We show that protein S7 K is longer by 24 amino acids than protein S7 B and that