Multiple internal repeats within protein S1 from the Escherichia coli ribosome

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Abstract
The complete sequence determination of protein S1, the largest protein from the Escherichia coli ribosome, revealed that it is composed of repeated internal duplications, mainly at the central region of the molecule which contains the mRNA‐binding domain [Eur. J. Biochem. (1982) 123, 37–53]. With the aid of computer programs the statistical significance of the internal repeats in S1 was proven. Auto‐comparison of the S1‐sequence showed that it is composed of 87‐residue strings with 44‐residue subunits: 3 strings (residues 189–447) are highly related; 3 strings (residues 13–188 and 448–533) are less but significantly related. Statistical analysis revealed a more distant relatedness for the 44‐residue subunits than for the 87‐residue strings. Protein S1 was compared to all other E. coli ribosomal proteins and to the 1100 primary structures listed in the last. Atlas of Protein Sequence and Structure (1978) showing parts of S1 distantly related with parts of several ribosomal proteins. However, distinct homologies between protein S1 and the other ribosomal proteins can be ruled out. The strongest repeats within the S1 sequence were mainly found corresponding to the mRNA‐binding domain. Distantly related partial sequences were also found with ribosome‐associated and nucleotide‐binding proteins, with some enzymes, with several peptide hormones and with contractile proteins.