Escherichia coli Frameshift Mutation Rate Depends on the Chromosomal Context but Not on the GATC Content Near the Mutation Site

Different studies have suggested that mutation rate varies at different positions in the genome. In this work we analyzed if the chromosomal context and/or the presence of GATC sites can affect the frameshift mutation rate in the Escherichia coli genome. We show that in a mismatch repair deficient background, a condition where the mutation rate reflects the fidelity of the DNA polymerization process, the frameshift mutation rate could vary up to four times among different chromosomal contexts. Furthermore, the mismatch repair efficiency could vary up to eight times when compared at different chromosomal locations, indicating that detection and/or repair of frameshift events also depends on the chromosomal context. Also, GATC sequences have been proved to be essential for the correct functioning of the E. coli mismatch repair system. Using bacteriophage heteroduplexes molecules it has been shown that GATC influence the mismatch repair efficiency in a distance- and number-dependent manner, being almost nonfunctional when GATC sequences are located at 1 kb or more from the mutation site. Interestingly, we found that in E. coli genomic DNA the mismatch repair system can efficiently function even if the nearest GATC sequence is located more than 2 kb away from the mutation site. The results presented in this work show that even though frameshift mutations can be efficiently generated and/or repaired anywhere in the genome, these processes can be modulated by the chromosomal context that surrounds the mutation site

Test results of HIRFL-CSR main ring electron cooling device

<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Electron cooling device for HIRFL-CSR main ring has been completed under the cooperation between BINP and IMP. It has three distinctive characters. Variable profile electron beam can be produced by the electron gun, the size and density distribution of electron beam can be changed. The parallelism of the magnetic field in the cooling section achieves less than 1 x 10(-5), in this case, the r. m. s angle deviations of the magnetic field line in horizontal and vertical direction are 7.838 x 10(-6) and 8.044 x 10(-6) respectively. The electron beam loss is reduced, the vacuum condition is improved, and the instability of the electron beam is suppressed becanse of using of electrostatic bending plate in the toroid. The beam profile and density distribution were measured in the testbench. The characters of the gun and collector were investigated. The main test results are presented in this paper.</span

PROTOTYPE OF AN ELECTRON COOLING DEVICE WITHOUT BENDING MAGNETS

The technical solution of a prototype of an electron cooling device without bending magnets is presented. The electron beam with a current of up to 1 A is formed in a ''hollow'' gun, accelerated up to 20 kV and its energy is recovered in a ''hollow'' collector with a current loss of less than 10-4. Preliminary beam quality tests are described

Longitudinal electron cooling experiments at HIRFL-CSRe

<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">At the heavy ion storage ring HIRFL-CSRe an electron cooler is operated to improve the beam conditions for experiments. The properties of cooled beams have been studied. The longitudinal beam dynamics during the cooling process was measured by a resonant Schottky detector. The dependencies of the parameters electron beam density and profile on cooling times were investigated. The friction force was measured directly with the aid of the high voltage system of the cooler and with the application of the beam bunching system as well. An experiment with bunched cold beam showed a dependence of the bunch length on the beam density. (C) 2015 Elsevier B.V. All rights reserved.</span

Research on the detuning system of a cooling electron beam for the dielectronic recombination experiment at CSRm

<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">A storage ring equipped with an electron cooler is an ideal platform for dielectronic recombination (DR) experiments. In order to fulfill the requirement of DR measurements at the main Cooler Storage Ring, a detuning system for the precision control of the relative energy between the ion beam and the electron beam has been installed on the electron cooler device. The test run using 7.0 MeV/u C6+ beam was performed with recording the Schottky spectra and the ion beam currents. The influence of pulse heights and widths of the detuning voltage on the ion beam was analyzed. For the small pulse height, the experimental results from the Schottky spectra were in good agreement with the theoretical results. The frequency shift in the Schottky spectra was significantly reduced for the short pulse width. For the large pulse height, an oscillation phenomenon was observed and some effective ways to reduce the oscillation were pointed out. The detailed description of the phenomenon and the theoretical model based on the plasma oscillation is discussed in this paper. The overall results show that the new detuning system works properly, and could fulfill the requirements of future DR experiments.</span

CRYSTAL: a storage ring for crystalline beams and other applications

The possibility of generating crystallized ion beams has always excited the interest of most people working on particle accelerators. The reason of this interest has manifold aspects: either a knowledge on a completely new research field or some of the applicative potentialities, connected with crystallinebeams, would justify a careful investigation on this content. The Conceptual Design of a low-energy heavy-ion storagering, called CRYSTAL, proposed for the experimental demonstration of crystallinebeams at Legnaro Laboratories is presented. Besides the study of crystallinebeams the CRYSTAL StorageRing (CSR) offers a large potential for fundamental research in nuclear, atomic and molecular physics. In this sense, the development of a second generation cooler ring with better lattice will give large possibilities to investigate more deeply in fundamental Physics

First recombination experiment of fluorine-like nickel ions at the main cooler storage ring

<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Absolute non-resonant recombination (RR) rate coefficients of Ni19+ ions were measured by employing the electron-ion merged-beams technique at the main cooler storage ring in Lanzhou. Using the electron cooler and energy detuning system, we obtained a narrow momentum spread (Delta p/p similar to 2 x 10(-4))and tuned precisely relative energies (minimum electron energy detuning step voltage 1 V) between electrons and ions. In addition, we compared the RR rate coefficients with the theoretical ones calculated by the self-consistent-field Dirac-Slater method, and found that they are in good agreement.</span

A storage ring for crystalline beam studies

The possibility of generating crystallized ion beams, i.e. beams whose particles are located at fixed positions, has always excited the interest of most people working on particle accelerators. The reason of this interest has many aspects: knowledge either of a completely new research field or of some of the applicative potentialities, connected with crystalline beams, would justify a careful investigation of this subject. After the successful exploitation of electron cooling in several heavy ion storage rings the possibility of generating crystalline ion beams became more realistic. New cooling methods, like laser cooling, give a further opportunity to reach an ultracold system of particles necessary for the state transition to the crystalline configuration. The conceptual design of a low-energy heavy-ion storage ring, called CRYSTAL, proposed for the experimental demonstration of crystalline beams at Legnaro Laboratories is presented. The physics of crystalline beams as well as the main criteria to design a storage ring suitable to crystallize ion beams are discussed. The effects of instabilities for space charge dominated beams, shear forces in dipole magnets and lattice periodicity breaking are also discussed in detail