Relief of polarity in E. coli depleted of 30S ribosomal subunits.

Summary Escherichia coli was depleted of ribosomes by a thermal shock at 47° C which quantitatively destroyed the 30S ribosomal subunits. During recovery in minimal medium at 30° C RNA is synthesized while protein synthesis resumes only after about 90 min. It is shown that lac mRNA is synthesized in the complete absence of ribosomal activity and hence RNA synthesis is not coupled to protein synthesis. Lac mRNA from a series of lac nonsense mutants was examined in both heated and untreated cells. It was found that the polar effect of nonsense mutation is relieved in the absence of ribosomes and that this relief is due to the synthesis of larger mRNA molecules. Since Rho remained active in thermally treated cells, premature termination at secondary signals within the lac operon must also depend on the presence of active ribosomes.Abbreviations used SSC 0.15 M Nacl, 0.015 M sodium citrate (pH 7.0) - mRNA messenger ribonucleic acid - IPTG isopropyl--D-thiogalactopyranoside - cAMP adenosine 3: 5-cyclic monophosphoric acid - LDS lithium dodecyl sulfate - TCA trichloroacetic acid The paper forms part of the first author's M.Sc. thesis