Primary structure of Escherichia coli ribosomal protein S1 and of its gene rpsA

The primary structure of protein S1, the largest protein component of the E. coli ribosome, has been elucidated by determining the amino acid sequence of the protein (from E. coli MRE600) and the nucleotide sequence of the S1 gene (rpsA, of a K-12 strain). The two methods gave results in perfect agreement except at two positions where possible strain-specific differences were found. Protein S1 (MRE600) is composed of 557 amino acid residues (no modified amino acids were detected) and has M(r) 61,159. The DNA sequence for protein S1 (K-12) suggests 556 amino acid residues. A computer survey of the sequence revealed three regions in S1 with a high degree of internal homology. The ribosome binding of domain of S1 (NH₂ terminus) does not show any preponderance of basic amino acids. The two cysteine and the majority of tryptophan residues of S1 as well as two of the three homologous regions are located in its middle region which contains the nucleic acid binding domain. The pattern of degenerate codon usage in the S1 gene is nonrandom and similar to that reported for other ribosomal protein genes.