Role of ribosomal protein S12 in peptide chain elongation: analysis of pleiotropic, streptomycin-resistant mutants of Escherichia coli

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Abstract
Some of the spontaneous streptomycin-resistant mutants of E. coli strain C600 exhibit pleiotropic effects in addition to the antibiotic resistance. These effects include decreased growth rates, reduced levels of certain enzymes and poor support of bacteriophage growth. One of these mutants, strain SM3, was studied further. The reduced growth rate of the mutant SM3 may be related to the reduction in relative amounts of ribosomes or to the reduction in the efficiency of ribosomes in protein synthesis. Measurements of .alpha.r, the differential synthesis rate of ribosomal protein, revealed that the protein synthesis efficiency of ribosomes from the mutant strain SM3 was reduced .apprx. 2-fold relative to that of the parent strain C600. Measurements of the induction lag for .beta.-galactosidase and of the synthesis time of several different MW classes of proteins indicated that the mutation resulted in a marked reduction in the peptide chain growth rate. This reduction in the chain growth rate probably accounted for most of the observed reduction in the growth rate of the mutant strain. The strA gene product, the S12 protein of the 30S subunit, is apparently involved in some aspect of protein chain elongation. Presumably this involvement occurs during the mRNA-directed binding of tRNA acid to the ribosome.