Lifetime of bacterial messenger ribonucleic acid

Lifetime of messenger ribonucleic acid for penicillinase synthesis in several strains of bacilli

1. Previous studies of penicillinase synthesis in Bacillus licheniformis showed that enzyme synthesis after the addition of actinomycin continues for far longer in the constitutive mutant 749/C than in the parental inducible strain (Yudkin, 1966). This result was interpreted as indicating a difference in the lifetime of specific messenger RNA in the two strains. Other bacilli have now been examined in an attempt to see whether this difference is general. 2. There was no difference in the lifetime of messenger RNA for penicillinase synthesis between an inducible and a constitutive strain of Bacillus cereus. 3. Three freshly isolated constitutive mutants of B. licheniformis also had short-lived messenger RNA, like their inducible parent. 4. A reinvestigation of mutant 749/C confirmed the original finding that, on treatment with actinomycin, it continued to synthesize penicillinase far longer than did its parent. 5. An inducible revertant of mutant 749/C was indistinguishable from the original inducible strain, and appeared to have lost both constitutivity and long-lived messenger RNA in the back mutation.

The regulatory process in the de-repression of enzyme synthesis. Alkaline phosphatase of Bacillus subtilis

1. The kinetics of de-repression of alkaline phosphatase in Bacillus subtilis were studied after the removal of P(i). Enzyme activity appeared about 10min. after removal of P(i), whereas ;enzyme-forming potential' appeared after 6min. 2. Protein synthesis is not impaired for at least 20min. on removal of P(i), but RNA synthesis is considerably diminished. 3. Adding chloramphenicol to cells without P(i), just at the time they start to make enzyme-forming potential, does not affect the differential rate of enzyme synthesis compared with total protein. Enzyme-forming potential accumulates to about normal levels in the presence of chloramphenicol, even though peptide-bond formation is inhibited by more than 95%. 4. Similar experiments performed with actinomycin C show more complex effects. Actinomycin initially prevents RNA synthesis and also the synthesis of enzyme-forming potential. After some minutes RNA synthesis resumes at a low rate, to be followed 4min. later by enzyme synthesis. Enzyme-forming potential can accumulate in the presence of actinomycin after the resumption of RNA synthesis. Protein synthesis, initially inhibited by actinomycin as a consequence of the effect on RNA synthesis, is later directly inhibited by actinomycin. 5. Adding actinomycin to de-repressed cells already making enzyme stops enzyme synthesis within 4-5min. Enzyme synthesis resumes, as before, 4min. after the resumption of RNA synthesis. 6. Adding P(i) together with actinomycin to de-repressed cells synthesizing enzyme does not result in a lower yield of enzyme compared with actinomycin alone. 7. Actinomycin is less effective an inhibitor of RNA and protein synthesis in P(i)-starved cells if P(i) is also added. 8. These results are discussed in view of the three main models for the regulation of enzyme induction: regulation at the level of transcription only, at translation only, or a coupled model in which transcription requires concomitant translation. It is concluded that the present evidence most powerfully supports the model of transcriptional regulation.

Catabolite repression of beta-galactosidase synthesis in Escherichia coli

1. Repression by glucose of beta-galactosidase synthesis is spontaneously reversible in all strains of Escherichia coli examined long before the glucose has all been consumed. The extent of recovery and the time necessary for reversal differ among various strains. Other inducible enzymes show similar effects. 2. This transient effect of glucose repression is observed in constitutive (i(-)) and permease-less (y(-)) cells as well as in the corresponding i(+) and y(+) strains. 3. Repression is exerted by several rapidly metabolizable substrates (galactose, ribose and ribonucleosides) but not by non-metabolized or poorly metabolized compounds (2-deoxyglucose, 2-deoxyribose, phenyl thio-beta-galactoside and 2-deoxyribonucleosides). 4. The transient repression with glucose is observed in inducible cells supplied with a powerful inducer of beta-galactosidase synthesis (e.g. isopropyl thio-beta-galactoside) but not with a weak inducer (lactose); in the latter instance glucose repression is permanent. Diauxic growth on glucose plus lactose can be abolished by including isopropyl thio-beta-galactoside in the medium. 5. In some strains phosphate starvation increases catabolite repression; in others it relieves it. Adenine starvation in an adenine-requiring mutant also relieves catabolite repression by glycerol but not that by glucose. Restoration of phosphate or adenine to cells starved of these nutrients causes a pronounced temporary repression. Alkaline-phosphatase synthesis is not affected by the availability of adenine. 6. During periods of transient repression of induced enzyme synthesis the differential rate of RNA synthesis, measured by labelled uracil incorporation in 2min. pulses, shows a temporary rise. 7. The differential rate of uracil incorporation into RNA falls during exponential growth of batch cultures of E. coli. This is equally true for uracil-requiring and non-requiring strains. The fall in the rate of incorporation has been shown to be due to a real fall in the rate of RNA synthesis. The significance of the changes in the rate of RNA synthesis is discussed. 8. A partial model of catabolite repression is presented with suggestions for determining the chemical identification of the catabolite co-repressor itself.

Protein synthesis by long-lived messenger ribonucleic acid in bacteria

1. Experiments were performed to investigate two hypotheses about the function of long-lived messenger RNA in bacteria. After RNA synthesis had been stopped by the addition of actinomycin, continuing protein synthesis was used as a measure of persistent messenger RNA. 2. The hypothesis that messenger RNA responsible for the synthesis of membrane protein is exceptionally long-lived was tested in experiments with protoplasts of Bacillus megaterium. However, this messenger RNA proved to be of approximately average stability. 3. The hypothesis that long-lived messenger RNA is responsible for the synthesis of constitutive proteins was tested by comparing the synthesis of penicillinase in an inducible and a constitutive strain of Bacillus licheniformis. After the addition of actinomycin, penicillinase synthesis continued for far longer in the constitutive than in the inducible strain. This difference is attributed to a difference in stability of the penicillinase-messenger RNA in the two strains, which does not extend to all messenger RNA indiscriminately. 4. A model is tentatively proposed to account for the altered stability of messenger RNA in the constitutive mutant.

Action of phyenethyl alcohol on the synthesis of macromolecules in Escherichia coli

Prevost, C. (University of California, Berkeley), and V. Moses. Action of phenethyl alcohol on the synthesis of macromolecules in Escherichia coli. J. Bacteriol. 91:1446-1452. 1966.-A kinetic study of the effects of various concentrations of phenethyl alcohol on the synthesis of ribonucleic acid (RNA), deoxyribonucleic acid (DNA), protein, and beta-galactosidase in Escherichia coli has confirmed that RNA synthesis, rather than DNA synthesis, is first and most affected by phenethyl alcohol. The presence of inducer did not protect beta-galactosidase synthesis from inhibition by phenethyl alcohol. Little preferential inhibition of beta-galactosidase synthesis was observed; this is in contrast to the severe catabolite repression which results from partial inhibition of total protein synthesis caused by chloramphenicol or starvation for a required amino acid. We found no evidence that messenger RNA synthesis was inhibited to a greater extent than total RNA synthesis.

Lifetime of bacterial messenger ribonucleic acid

Moses, V. (University of California, Berkeley), and M. Calvin. Lifetime of bacterial messenger ribonucleic acid. J. Bacteriol. 90:1205-1217. 1965.-When cells from a stationary culture of Escherichia coli were placed in fresh medium containing inducer for beta-galactosidase, growth, as represented by increase in turbidity and by total protein synthesis, started within 30 sec. By contrast, beta-galactosidase synthesis was greatly delayed compared with induction during exponential growth. Two other inducible enzymes (d-serine deaminase and l-tryptophanase) and one repressible enzyme (alkaline phosphatase) showed similar lags. The lags were not due to catabolite repression. They could not be reduced by pretreatment of the culture with inducer, or by supplementing the fresh medium with amino acids or nucleotides. The lag was also demonstrated by an i(-) mutant constitutive for beta-galactosidase synthesis. An inhibitor of ribonucleic acid (RNA) synthesis, 6-azauracil, preferentially inhibited beta-galactosidase synthesis compared with growth in both inducible and constitutive strains. Puromycin, an inhibitor of protein synthesis, acted as an inhibitor at additional sites during the induction of beta-galactosidase synthesis. No inhibition of the reactions proceeding during the first 20 sec of induction was observed, but puromycin seemed to prevent the accumulation of messenger RNA during the period between 20 sec and the first appearance of enzyme activity after 3 min. It is suggested that these observations, together with many reports in the literature that inducible enzyme synthesis is more sensitive than total growth to some inhibitors and adverse growth conditions, can be explained by supposing that messenger RNA for normally inducible enzymes is biologically more labile than that for some normally constitutive proteins. The possible implications of this hypothesis for the achievement of cell differentiation by genetic regulation of enzyme synthesis are briefly discussed.