No abstract

The expression of stable RNA (rRNA and tRNA) genes and the concentration of guanosine tetraphosphate (ppGpp) were measured in an isogenic pair of relA+ and relA derivatives of Escherichia coli B/r. The cells were either growing exponentially at different rates or subject to amino acid starvation when they were measured. The specific stable RNA gene activity (rslr,, the rate of rRNA and tRNA synthesis relative to the total instantaneous rate of RNA synthesis) was found to decrease from 1.0 at a ppGpp concentration of 0 (extrapolated value) to 0.24 at saturating concentrations of ppGpp (above 100 pmoles per optical density at 460 nm unit of cell mass). The same relationship between the rlr, ratio and ppGpp concentration was obtained independent of the physiological state of the bacteria (i.e., independent of the growth rate or of amino acid starvation) and independent of the relA allele. It can be concluded that ppGpp is an effector for stable RNA gene control and that stable RNA genes are not controlled by factors other than the ppGpp-mediated system. The results were shown to be qualitatively and quantitatively consistent with data on in vitro rRNA gene control by ppGpp, and they were interpreted in the light of reported ideas derived from those in vitro experiments.In Escherichia coli, the rates of ribosome and tRNA synthesis are correlated with the intracellular concentration of guanosine tetraphosphate (ppGpp). At low levels of ppGpp, ribosome and tRNA synthesis are stimulated (relaxed response); at high levels of ppGpp, ribosome and tRNA synthesis are inhibited (stringent response) (10, 21). In vitro experiments with purified RNA polymerase and DNA templates containing rRNA genes suggest that ppGpp interacts with the RNA polymerase enzyme (36,42) and affects its conformation (37). The enzyme in one conformation was assumed to have a higher affinity for stable RNA (rRNA, tRNA) promoters, whereas that in another conformation has a higher affinity for bulk messenger RNA (mRNA) promoters (37). In vivo results about the role of ppGpp have been ambiguous, since examples have been reported in Wyhich the normal correlation between ppGpp and the stringent or relaxed response did not seem to hold (12,14,24,33). For that reason, the significance of ppGpp as an effector controlling stable RNA synthesis in vivo has been questioned (12), and it was thought that other factors (e.g., guanosine 5'-diphosphate-3'-monophosphate [ppGp]) play a major role in controlling rRNA and tRNA synthesis in vivo (11).One anomalous response of RNA synthesis to ppGpp was observed after temperature upshift (12). We have recently reinvestigated the temperature effects on RNA synthesis (29; J. Ryals, R. Little, and H. Bremer, J. Bacteriol., in press) and found that, in this case at least, the response only appeared to be anomalous since the specific stable RNA gene activity was quite normal (decreased during ppGpp accumulation) but was obscured by a nonspecific increase in the RNA chain elongation rate due to the higher temperature. This study t...

The potent anabolic effects of the beta 2-adrenoceptor agonist clenbuterol on skeletal muscle have been reported to be independent of actions on beta-adrenoceptors. In the present study clenbuterol, presented to rats in the diet (4 mg/kg), caused significant increases in gastrocnemius muscle mass, protein, and RNA content and a decrease in epididymal fat pad mass. These effects were not mimicked by oral administration of the beta 2-adrenoceptor agonist salbutamol even at high dose (52 mg/kg diet), and the effects of clenbuterol were not inhibited by addition of DL-propranolol (200 mg/kg diet). However, the selective beta 2-antagonist ICI-118,551 (200 mg/kg diet) reversed the anabolic effects of clenbuterol, and a high dose of DL-propranolol (1,000 mg/kg diet) also inhibited these actions of clenbuterol. Furthermore, continuous infusion of salbutamol (1.15 mg.kg body wt-1.day-1) via miniosmotic pumps did cause significant increases in muscle mass, protein, and RNA content. These results indicate that the anabolic effects of clenbuterol are dependent on interaction with the beta 2-adrenoceptor. However, a long duration of action appears to be required to induce the anabolic effects of beta 2-agonists.

Endotracheal intubation in the field does not improve outcome in trauma patients who present without an acutely lethal traumatic brain injury.