Studies of newly synthesized ribosomal ribonucleic acid of Escherichia coli

Antisense RNA: effect of ribosome binding sites, target location, size, and concentration on the translation of specific mRNA molecules

A series of plasmids were constructed to generate RNA complementary to the beta-galactosidase messenger RNA under control of the phage lambda PL promoter. These plasmids generate anti-lacZ mRNA bearing or lacking a synthetic ribosome binding site adjacent to the lambda PL promoter and/or the lacZ ribosome binding site in reverse orientation. Fragments of lacZ DNA from the 5' and/or the 3' region were used in these constructions. When these anti-mRNA molecules were produced in Escherichia coli 294, maximal inhibition of beta-galactosidase synthesis occurred when a functional ribosome binding site was present near the 5' end of the anti-mRNA and the anti-mRNA synthesized was complementary to the 5' region of the mRNA corresponding to the lacZ ribosome binding site and/or the 5'-coding sequence. Anti-mRNAs producing maximal inhibition of beta-galactosidase synthesis exhibited an anti-lacZ mRNA:normal lacZ mRNA ratio of 100:1 or higher. Those showing lower levels of inhibition exhibited much lower anti-lacZ mRNA:normal lacZ mRNA ratios. A functional ribosome binding site at the 5'-end was found to decrease the decay rate of the anti-lacZ mRNAs. In addition, the incorporation of a transcription terminator just downstream of the antisense segment provided for more efficient inhibition of lacZ mRNA translation due to synthesis of smaller and more abundant anti-lacZ mRNAs. The optimal constructions produced undetectable levels of beta-galactosidase synthesis.

Association of nascent ribosomal ribonucleic acid with polyribosomes in Escherichia coli

Sedimentation distributions of rapidly labeled ribonucleic acid (RNA) in extracts prepared from cells labeled for 60 s or less with [3H]uridine showed that the immature ribosome precursor particles themselves have an RNA precursor which sediments with polyribosomes and 70s ribosomes. In extracts prepared from cultures labeled for 30 s, the fraction of labeled RNA which did not sediment with polyribosomes was much less than the fraction which was ribosomal RNA (rRNA). Rapidly labeled RNA associated with polyribosomes had a nucleotide base composition consistent with the presence of rRNA, and was shown by RNA-deoxyribonucleic acid hybridization to contain 30 to 40% rRNA. Nascent rRNA is thus associated with polyribosomes during its transcription. The sedimentation distribution of rapidly labeled 16s and 23s rRNA showed that these molecules are separated during transcription and associated with different polyribosomes.

Effect of cyclic guanosine 3,5-monophosphate on the synthesis of enzymes sensitive to caatabolite repression in intact cells of Escherichia coli

Cyclic guanosine 3',5'-monophosphate inhibits the synthesis of beta-galactosidase and tryptophanase in cultures of Escherichia coli growing in minimal media with glucose or glycerol as the carbon source. Cyclic guanosine 3',5'-monophosphate acts at the transcriptional level in the lac operon, it exerts its action at the promoter site of the operon, and requires the presence of functional cyclic adenosine 3',5'-monophosphate receptor protein.

The control of ribonucleic acid synthesis in bacteria. The synthesis and stability of ribonucleic acids in relaxed and stringent amino acid auxotrophs of Escherichia coli

The biosynthesis and stability of various RNA fractions was studied in RC(str) and RC(rel) multiple amino acid auxotrophs of Escherichia coli. In conditions of amino acid deprivation, RC(str) mutants were labelled with exogenous nucleotide bases at less than 1% of the rate found in cultures growing normally in supplemented media. Studies by DNA-RNA hybridization and by other methods showed that, during a period of amino acid withdrawal, not more than 60-70% of the labelled RNA formed in RC(str) mutants had the characteristics of mRNA. Evidence was obtained for some degradation of newly formed 16S and 23S rRNA species to heterogeneous material of lower molecular weight. This led to overestimations of the mRNA content of rapidly labelled RNA from such methods as simple examination of sucrose-density-gradient profiles. In RC(rel) strains the absolute and relative rates of synthesis of the various RNA fractions were not greatly affected. However, the stability of about half of the mRNA fraction was increased in RC(rel) strains during amino acid starvation, giving kinetics of mRNA labelling and turnover that were identical with those found in either RC(str) or RC(rel) strains inhibited by high concentrations of chloramphenicol. Coincidence hybridization techniques showed that the mRNA content of amino acid-starved RC(str) auxotrophs was unchanged from that found in normally growing cells. In contrast, RC(rel) strains deprived of amino acids increased their mRNA content about threefold. In such cultures the mRNA content of accumulating newly formed RNA was a constant 16% by wt.

Dissociation of Lac messenger ribonucleic acid transcription from translation during recovery from inhibition of protein synthesis

Studies were made of the synthesis of Lac messenger ribonucleic acid (mRNA) by Escherichia coli in the absence of protein synthesis and of the coupling of transcription of lac operon to translation. Lac mRNA was not synthesized in the presence of chloramphenicol, and its synthesis steadily decreased during K(+) deprivation and treatment with puromycin. Since under these conditions total mRNA synthesis is not inhibited it is suggested that the control of Lac mRNA is distinct from that which regulates total mRNA synthesis. Lac mRNA synthesized during recovery from K(+) starvation or from chloramphenicol inhibition is not translated into functional enzyme, suggesting translational control over beta-galactosidase synthesis.

The control of ribonucleic acid synthesis in bacteria. Steady-state content of messenger ribonucleic acid in Escherichia coli M.R.E. 600

1. The technique of DNA-RNA hybridization was used to follow changes in the amount and average lifetime of unstable messenger RNA in Escherichia coli M.R.E. 600 over a wide range of different growth conditions. The method of analysis was based on the kinetics of incorporation of exogenous labelled nucleic acid bases into the RNA of steadily growing cultures, as described by Bolton & McCarthy (1962). 2. The ratio of the average lifetime of messenger RNA to the mean generation time of E. coli cultures was constant over the temperature range 25-45 degrees C in a given medium, but the constant varied with the nature of the growth medium. For cultures growing in sodium lactate-salts or glucose-salts media the ratio was 0.046+/-0.005 and in enriched broth it was 0.087+/-0.009. Measurements of the amounts of transfer RNA, ribosomal RNA and messenger RNA were also made. The results confirmed earlier reports that the ratio of the amount of messenger RNA to the amount of ribosomes in the cells is virtually constant. On the other hand, the ratio of the amount of transfer RNA to the amount of ribosomal RNA decreased with increasing growth rate at a given temperature. 3. In cultures at temperatures higher than necessary for optimum rates of growth the average lifetime of messenger RNA lengthened in harmony with the increased time required for cell division. It seems that suboptimum growth rates at higher temperatures cannot be explained simply as a combination of increased rates of synthesis and breakdown of messenger RNA with a grossly decreased efficiency of translation. The absolute rate of messenger RNA synthesis was lowered, and its amount in the cells was typical of all other cultures grown at lower temperatures in the same medium. 4. The rate of entry of exogenous labelled uracil into unstable messenger RNA and stable ribosomal RNA was constant in all media at all temperatures in the approximate ratio 1:2. In media supporting a lower rate of growth, e.g. lactate-salts or glucose-salts media, the messenger RNA fraction constituted 2.2+/-0.3% of the total cellular RNA. In enriched broth 3.6+/-0.3% of the total RNA was messenger.