Transcription analysis of the stretomyces-coelicolor A3(2) ribosomal-RNA operon

Microbial Biotechnolog

Functional studies of elongation factor Tu from Escherichia coli : Site-directed mutagenesis and antibiotic actio

This PhD thesis describes several studies into the structure and function of Escherichia coli Elongation Factor Tu (EF-Tu). EF-Tu plays a central role in the bacterial protein synthesis machinery as the carrier of "coded building blocks" for protein synthesis, aminoacylated tRNA (aa-tRNA). Without EF-Tu, fast and accurate protein synthesis would be impossible. It not only binds and carries the aa-tRNA to the ribosome, it also plays a role in the selection of the correct aa-tRNA for the codon of the messenger RNA (mRNA) currently being decoded. This selection process, which takes place on the ribosome, is supported by hydrolysis of a GTP molecule bound to the EF-Tu-aa-tRNA complex. Once the GTP is hydrolyzed to GDP, the EF-Tu changes conformation and detaches from both the aa-tRNA and the ribosome. The aa-tRNA, if it matches the anticodon on the mRNA, will progress to the incorporation of its activated amino acid into the growing protein chain. If the anticodon does not match, however, proofreading will (r)eject it from the ribosome. There are indications that a second EF-Tu, or at least GTP hydrolysis by a second EF-Tu is involved in this process, but it is not understood how. The work in this thesis is mostly centered on understanding the role of several amino acid residues of EF-Tu in the interaction with the GTP or GDP nucleotide, the catalysis of GTP hydrolysis but EF-Tu and the mechanism by which this only accelerated five orders of magnitude on the ribosome. It leads to a number of interesting conclusions that shed light on the problem, but cannot explain the "triggered catalysis" mechanism.</p

Functional studies of elongation factor Tu from Escherichia coli : Site-directed mutagenesis and antibiotic actio

This PhD thesis describes several studies into the structure and function of Escherichia coli Elongation Factor Tu (EF-Tu). EF-Tu plays a central role in the bacterial protein synthesis machinery as the carrier of "coded building blocks" for protein synthesis, aminoacylated tRNA (aa-tRNA). Without EF-Tu, fast and accurate protein synthesis would be impossible. It not only binds and carries the aa-tRNA to the ribosome, it also plays a role in the selection of the correct aa-tRNA for the codon of the messenger RNA (mRNA) currently being decoded. This selection process, which takes place on the ribosome, is supported by hydrolysis of a GTP molecule bound to the EF-Tu-aa-tRNA complex. Once the GTP is hydrolyzed to GDP, the EF-Tu changes conformation and detaches from both the aa-tRNA and the ribosome. The aa-tRNA, if it matches the anticodon on the mRNA, will progress to the incorporation of its activated amino acid into the growing protein chain. If the anticodon does not match, however, proofreading will (r)eject it from the ribosome. There are indications that a second EF-Tu, or at least GTP hydrolysis by a second EF-Tu is involved in this process, but it is not understood how. The work in this thesis is mostly centered on understanding the role of several amino acid residues of EF-Tu in the interaction with the GTP or GDP nucleotide, the catalysis of GTP hydrolysis but EF-Tu and the mechanism by which this only accelerated five orders of magnitude on the ribosome. It leads to a number of interesting conclusions that shed light on the problem, but cannot explain the "triggered catalysis" mechanism.Ecole Polytechnique, Palaiseau, FrankrijkMacromolecular Biochemistr

Identification of the site where the electron transfer chain of plant mitochondria is stimulated by electrostatic charge screening.

Modular kinetic analysis was used to determine the sites in plant mitochondria where charge-screening stimulates the rate of electron transfer from external NAD(P)H to oxygen. In mitochondria isolated from potato (Solanum tuberosum L.) tuber callus, stimulation of the rate of oxygen uptake was accompanied by a decrease in the steady-state reduction level of coenzyme Q, and by a small decrease in the steady-state reduction level of cytochrome c. Modular kinetic analysis around coenzyme Q revealed that stimulation of the rate was due to stimulation of quinol oxidation via the cytochrome pathway (cytochrome b

How extreme is a extreme climatic event to a subarctic peatland springtail community?

Extreme climate events are increasing in frequency and duration and may directly impact belowground foodwebs and the activities of component soil organisms. The soil invertebrate community, which includes keystone decomposers, might respond to these newly induced soil microclimate conditions by shifts in density, species composition, spatial patterning and/or functional traits.To test if and how short-term extreme climatic conditions alter the structure, the vertical stratification and the community weighted trait means of the springtail (Collembola) community in sub-arctic peatbogs, we experimentally subjected Sphagnum peat cores in a field setting to factorial treatments of elevated temperature and episodically increased moisture content.The large precipitation peaks did not affect the springtail community, but an average soil temperature increase of 4 °C halved its density in the shallower peat layers, mainly caused by the reduced dominance of Folsomia quadrioculata. A hypothesized net downward shift of the surface-dwelling springtail community, however, was not observed. We observed species-specific responses to warming but the overall community composition in subsequent organic layers was not significantly altered. Although the effects of an extreme warming event on density, species composition and vertical stratification pattern seemed subtle, functional trait analysis revealed directional community responses, i.e. an overall increase of soil-dwelling species due to warming, even though warming did not alter layer-specific community weighted trait means.We suggest that subtle changes in moisture conditions, due to increased evapotranspiration, have decreased typically surface-dwelling species relative to soil-dwelling species. The extent to which this directional change in the community is maintained after an extreme event, and its costs for the community's resilience to multiple sequential extreme events will consequently determine its longer-term effects on the community and on ecosystem functioning. © 2013 Elsevier Ltd