title: Ribosomal protein S4 acts in trans as a translational repressor to regulate expression of the alpha operon in Escherichia coli.
abstract: Ribosomal protein (r-protein) S4 is the translational repressor which regulates the synthesis rates of r-proteins whose genes are in the alpha operon: r-proteins S13, S11, S4, and L17. In a strain having a mutation in the gene for r-protein S4 (rpsD), the mutant S4 fails to regulate expression of the alpha operon, resulting in specific and significant overproduction of r-proteins S13, S11, and S4. This confirms and extends similar observations made with rpsD mutants (M. O. Olsson and L. A. Isaksson, Mol. Gen. Genet. 169:271-278, 1979) before post-transcriptional regulation of r-protein synthesis was proposed and is consistent with the established regulatory role of r-protein S4. The rpsD mutant has been used to study the question of whether regulatory r-proteins function in trans or strictly in cis as translational repressors. The mutant strain was lysogenized with one or two specialized transducing phages carrying a wild-type S4 gene to obtain strains which were diploid or triploid with respect to the alpha operon. The wild-type and mutant forms of S4 were separated by two-dimensional polyacrylamide gel electrophoresis, which allowed accurate measurement of the relative contributions of r-proteins from different alpha operons within a single cell. We found that expression of r-proteins from the chromosomal alpha operon containing the rpsD allele was reduced when the wild-type S4 was present, with the effect being greater in the triploid strain than in the diploid strain. We conclude that the wild-type S4 acts in trans as a translational repressor to regulate expression from the chromosomal alpha operon.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D009154:Mutation; D009876:Operon; D011003:Ploidies; D014176:Protein Biosynthesis; D012269:Ribosomal Proteins / Q000235:genetics*; D013045:Species Specificity; D014158:Transcription, Genetic; D014161:Transduction, Genetic
chemical_list: D004269:DNA, Bacterial; D004279:DNA, Viral; D012269:Ribosomal Proteins; C031798:ribosomal protein S4