3,151 research outputs found
The kinetic mechanism of bacterial ribosome recycling.
Bacterial ribosome recycling requires breakdown of the post-termination complex (PoTC), comprising a messenger RNA (mRNA) and an uncharged transfer RNA (tRNA) cognate to the terminal mRNA codon bound to the 70S ribosome. The translation factors, elongation factor G and ribosome recycling factor, are known to be required for recycling, but there is controversy concerning whether these factors act primarily to effect the release of mRNA and tRNA from the ribosome, with the splitting of the ribosome into subunits being somewhat dispensable, or whether their main function is to catalyze the splitting reaction, which necessarily precedes mRNA and tRNA release. Here, we utilize three assays directly measuring the rates of mRNA and tRNA release and of ribosome splitting in several model PoTCs. Our results largely reconcile these previously held views. We demonstrate that, in the absence of an upstream Shine-Dalgarno (SD) sequence, PoTC breakdown proceeds in the order: mRNA release followed by tRNA release and then by 70S splitting. By contrast, in the presence of an SD sequence all three processes proceed with identical apparent rates, with the splitting step likely being rate-determining. Our results are consistent with ribosome profiling results demonstrating the influence of upstream SD-like sequences on ribosome occupancy at or just before the mRNA stop codon
Axisymmetric polydimethysiloxane microchannels for in vitro hemodynamic studies
The current microdevices used for biomedical research are often manufactured using microelectromechanical systems (MEMS) technology. Although it is possible to fabricate precise and reproducible rectangular microchannels using soft lithography techniques, this kind of geometry may not reflect the actual physiology of the microcirculation. Here, we present a simple method to fabricate circular polydimethysiloxane (PDMS) microchannels aiming to mimic an in vivo microvascular environment and suitable for state-of-the-art microscale flow visualization techniques, such as confocal ”PIV/PTV. By using a confocal ”PTV system individual red blood cells (RBCs) were successfully tracked trough a 75 ”m circular PDMS microchannel. The results show that RBC lateral dispersion increases with the volume fraction of RBCs in the solution, i.e. with the hematocrit
On the distribution of 1550-nm photon pairs efficiently generated using a periodically poled lithium niobate waveguide
We report on the generation of photon pairs in the 1550-nm band suitable for
long-distance fiber-optic quantum key distribution. The photon pairs were
generated in a periodically poled lithium niobate waveguide with a high
conversion-efficiency. Using a pulsed semiconductor laser with a pulse rate of
800 kHz and a maximum average pump power of 50 muW, we obtained a coincidence
rate of 600 s^-1. Our measurements are in agreement with a Poissonian
photon-pair distribution, as is expected from a comparison of the coherence
time of the pump and of the detected photons. An average of 0.9 photon pairs
per pulse was obtained.Comment: 12 pages, 3 figure
Chemical Effects on KÎČ/Kα X-Ray Intensity Ratio for 97mTc and 95mTc
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Chemiluminescence emission in cholesteric liquid crystalline core-shell microcapsules
Chemiluminescence behaviour in the core region of water/oil/water double emulsion droplets with cholesteric liquid crystalline (CLC) middle phase (CLC core-shell microcapsules) was demonstrated. We successfully fabricated CLC core-shell microcapsules containing an aqueous luminol solution as the inner phase using a microfluidic device, in which the helical axis of the CLC phase is normal to the surface. The CLC core-shell microcapsules proved to be a plausible candidate for highly sensitive HâOâ sensors because of the omnidirectional photonic structures of the CLC phase.Iwai Y., Kaji H., Uchida Y., et al. Chemiluminescence emission in cholesteric liquid crystalline core-shell microcapsules. Journal of Materials Chemistry C 2, 4904 (2014); https://doi.org/10.1039/c4tc00699b
Calculations of Branching Ratios for Radiative-Capture, One-Proton, and Two-Neutron Channels in the Fusion Reaction Bi+Zn
We discuss the possibility of the non-one-neutron emission channels in the
cold fusion reaction Zn + Bi to produce the element Z=113. For
this purpose, we calculate the evaporation-residue cross sections of
one-proton, radiative-capture, and two-neutron emissions relative to the
one-neutron emission in the reaction Zn + Bi. To estimate the
upper bounds of those quantities, we vary model parameters in the calculations,
such as the level-density parameter and the height of the fission barrier. We
conclude that the highest possibility is for the 2n reaction channel, and its
upper bounds are 2.4 and at most less than 7.9% with unrealistic parameter
values, under the actual experimental conditions of [J. Phys. Soc. Jpn. {\bf
73} (2004) 2593].Comment: 6 pages, 4 figure
Vitamin D, a modulator of musculoskeletal health in chronic kidney disease
The spectrum of activity of vitamin D goes beyond calcium and bone homeostasis, and growing evidence suggests that vitamin
D contributes to maintain musculoskeletal health in healthy subjects as well as in patients with chronic kidney disease (CKD),
who display the combination of bone metabolism disorder, muscle wasting, and weakness. Here, we review how vitamin D
represents a pathway in which bone and muscle may interact. In vitro studies have confirmed that the vitamin D receptor
is present on muscle, describing the mechanisms whereby vitamin D directly affects skeletal muscle. These include genomic
and nonâgenomic (rapid) effects, regulating cellular differentiation and proliferation. Observational studies have shown that
circulating 25âhydroxyvitamin D levels correlate with the clinical symptoms and muscle morphological changes observed in
CKD patients. Vitamin D deficiency has been linked to low bone formation rate and bone mineral density, with an increased
risk of skeletal fractures. The impact of low vitamin D status on skeletal muscle may also affect muscle metabolic pathways,
including its sensitivity to insulin. Although some interventional studies have shown that vitamin D may improve physical
performance and protect against the development of histological and radiological signs of hyperparathyroidism, evidence is
still insufficient to draw definitive conclusions
Global cellular regulation including cardiac function by post-translational protein arginylation.
In this issue a very significant contribution to cardiology describing critical roles of ATE1 appears by Kurosaka et al. [1]. In view of this paper, as the discoverers of ATE1, we have been asked to contribute an article (editorial) regarding ATE1 (enzyme which transfers arginine from arginyl tRNA to protein acceptors). This short article consists of three sections: 1) a historical anecdote describing how ATE1 was discovered; 2) its possible role in aging and cellular transformation, and most importantly; 3) its role in the development and maintenance of cardiac activity. The last section has direct bearing to the Kurosaka et al. paper.
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