Ribosomal protein S1 influences trans-translation in vitro and in vivo

When the bacterial ribosome stalls on a truncated mRNA, transfer–messenger RNA (tmRNA) acts initially as a transfer RNA (tRNA) and then as a messenger RNA (mRNA) to rescue the ribosome and add a peptide tag to the nascent polypeptide that targets it for degradation. Ribosomal protein S1 binds tmRNA but its functional role in this process has remained elusive. In this report, we demonstrate that, in vitro, S1 is dispensable for the tRNA-like role of tmRNA but is essential for its mRNA function. Increasing or decreasing the amount of protein S1 in vivo reduces the overall amount of trans-translated proteins. Also, a truncated S1 protein impaired for ribosome binding can still trigger protein tagging, suggesting that S1 interacts with tmRNA outside the ribosome to keep it in an active state. Overall, these results demonstrate that S1 has a role in tmRNA-mediated tagging that is distinct from its role during canonical translation

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The 10B(n,α) reaction cross-section is a well-established neutron cross-section standard for incident neutron energies up to 1 MeV. However, above this energy limit there are only scarce direct (n,α) measurements available and these few experimental data are showing large inconsistencies with each other. These discrepancies are reflected in the evaluated data libraries: ENDF/B-VII.1, JEFF-3.1.2 and JENDL-4.0 are in excellent agreement up to 100 keV incident neutrons, whereas the 10B(n,α) data in the different libraries show large differences in the MeV region. To address these inconsistencies, we have measured the cross section of the two branches of the 10B(n,α) reaction for incident neutron energies up to 3 MeV. We present here the 10B(n,α) and the 10B(n,α1γ) reactions cross section data, their branching ratio and the total 10B(n,α) reaction cross section. The measurements were conducted with a dedicated Frisch-grid ionization chamber installed at the GELINA pulsed neutron source of the EC-JRC. We compare our results with existing experimental data and evaluations

The CIELO collaboration: Progress in international evaluations of neutron reactions on Oxygen, Iron, Uranium and Plutonium

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies – 16O, 56Fe, 235,8U and 239Pu – with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality

The Cross-section of the 10B(n,alpha)7Li Reaction Measured in the MeV Energy Range

The excitation function of the 10B(n,alpha)7Li reaction was measured between 1.5 MeV and 5.6 MeV within the frame of the IAEA Coordinated Research project (CRP) on "Improvement of the Standard Cross Sections for Light Elements";. An ionisation chamber and signal digitisation were used for the spectrometry of the reaction products, which were forwards emitted by bombarding a thin boron target with neutrons produced at the IRMM Van de Graff accelerator. The neutron flux was determined by measuring the backwards emitted fission fragments from a 238U sample mounted in a back-to-back geometry relative to the boron target. The highlight of this study was the discovery of the kinematic effect of particle leaking, which is very important for the accurate determination of the number of the boron reaction events. The experiment is described and the results are discussed and compared with evaluations and experimental data of other groups.JRC.D.5-Neutron physic

The Effect of Particle leaking and its Implications for Measurements of the (n,alpha) reaction on Light Elements Using Ionisation Chambers

A new technique for the spectrometry of (n,alpha) reactions on light elements at MeV energies has been developed and successfully used for the measurement of the 10B(n,alpha)7Li reaction at the 7MV Van de Graaff accelerator of IRMM. The basic elements of the new method are a gridded ionisation chamber, a fast waveform digitizer and advanced off-line analysis. The powerful data visualistion allowed the discovery of the effect of particle leaking. Particle leaking arises from the simultaneous emision of reaction products in forwards angles and the inablity of the detector to resolve multiple particles. It is an inherent property of all GIC spectrometers used for the study of (n,charged particle) reactions on light-element solid targets. The measurement of the cross section strongly benefits from it but the determination of other measurables is negatively affected. Cross sections at seven energies between 1.5 MeV and 3.8 MeV have been obtained using the new technique. Compared to evaluations the IRMM cross sections are close to the JENDL 3.2 and JEF 2.2 but strongly deviate from the ENDF/B-VI data with the exception of very good agreement at 2.5 MeV. Forwards anagular distrivbutions are truncated at large emission angles by the effect of particle leaking and look like depleted of reaction products between a kinematically determined angle theta0 and 90°. it is shown that all values of the branching ratio alpha0/alpha1 of the 10B(n,alpha)7Li reaction published up to now in refereed journals and obtained by using ionisation chambers and face to face surface barrier detectors contain inaccuracies caused by particle leaking which has not been considered.JRC.D.5-Neutron physic

The Effect of Particle Leaking and its Implications for Measurements of the (n,alpha) Reaction on Light Elements Using Ionisation Chambers.

Abstract not availableJRC.D-Institute for Reference Materials and Measurements (Geel

Novel 4π Detection System for the Measurement of the 6Li(n,α)3H Reaction Cross-Section

A dedicated one-dimensional Time Projection Chamber (1D-TPC) was designed and produced at IRMM to determine the 6Li(n,α)3H cross section, in the 0.4-2.8 MeV energy range, aiming at 5% accuracy. The basic TPC components were a twin gridded ionisation chamber (GIC) with interwired electrodes and fast digitisation of the anode and cathode signals. The energy of both reaction products emitted from a thin 6LiF sample at the common TPC cathode was measured. A Kr(97%)CO2(3%) mixture was used as the detector gas at a pressure up to 3.5 bar. A 238U sample mounted on the cathode of an ionisation chamber without grid was used as the neutron flux monitor. Special care was taken to reduce the experimental sources of uncertainty. The beam-monitor 238U sample was characterised at IRMM by low-geometry α-counting with an accuracy of 0.1%. A 6Li sample was produced at IRMM by vacuum evaporation of 6LiF onto transparent aluminium backing. The number of 6Li atoms will be measured via Thermal Neutron Depth Profiling with an expected accuracy of 2% with respect to an IRMM Standard Reference Material. First test measurements were performed using a monoenergetic neutron beam produced by the T(p,n)3He reaction at the IRMM 7MV Van de Graaff accelerator. The experimental method and preliminary results are presented.JRC.D.4-Nuclear physic

Preparation of 6LiF deposits and characterisation via Monte Carlo simulations and Neutron Depth Profiling

The Institute for Reference Materials and Measurements (IRMM) is measuring the 6Li(n,t)4He cross section aiming at extending its status of standard over the MeV energy range. We developed a protocol to stretch-mount 0.75 micronmeter, 1.5 micronmeter, 8 micronmeter, and 20 micronmeter thick aluminium foils onto 0.5 mm thick tantalum rings. 6LiF samples were produced by depositing, by vacuum evaporation onto the aluminium backings, a layer of lithium fluoride 95.5% enriched in 6Li. We engineered dedicated tools and containers to handle and transport the resulting samples. These were characterised first at IRMM by differential weighing, then by Neutron Depth Profiling (NDP) at the TU Delft. These two measurements were found to be consistent for a selected sample, probed by a thermal neutron beam in three different regions to measure the 6LiF layer thickness and uniformity (defined as variation of the thickness relative to its average). The latter was found to be 0.8%, and the 6Li thickness to be 7.30 +/- 0.12, 7.35 +/- 0.12, and 7.29 +/- 0.12 micronmeter/cm2 in the three regions. We performed Monte Carlo simulations to estimate the uniformity of the 6LiF layer, and benchmarked the calculation against the NDP measurements. They were consistent with respect to the deposit uniformity although the simulations were found to overestimate the thickness of the layer.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Particle Leaking, Cross-Section Ratio 10B(n, )/238U(n,fission), and Excitation Function of the Reaction 10B(n, )7Li at MeV Energies

The 10B(n, )7Li reaction was studied in the energy range between 1.5 MeV and 5.6 MeV at the 7-MV Van de Graaff accelerator of IRMM by using a gridded ionisation chamber, signal digitisation, and an intrinsic 238U neutron monitor. The aim was to obtain accurate data for the IAEA Coordinated Research Project (CRP) on the improvement of standard cross sections for light elements. The effect of particle leaking was discovered and its implications investigated. The determination of the cross section delta( alpha0+alpha 1) strongly benefits from it but measurements of angular distributions, individual cross sections delta(alpha 0) and delta( alpha1), and the branching ratio alpha0/ alpha1 are negatively affected. The correct number of reaction events was obtained by identification of unknown particle signatures in the energy spectra as 10B(n,alpha)7Li events in the form of quasi 7Li+ alpha particles created by particle leaking. The cross-section ratio 10B(n,alpha)7Li/238U(n,fission) was measured and the excitation function of 10B(n,alpha)7Li determined by simultaneously detecting the charged particles from the boron disintegration in the forward hemisphere and the 238U fission fragments in the backward hemisphere. The IRMM cross sections are compared to experimental data of other groups and to predictions of the ENDF/B-VI.8, JENDL-3.3, and JEF-2.2 evaluations.JRC.D.5-Neutron physic