Dynamics of an Electron Bunch Accelerated by a Wakefield

The energy characteristics of an electron bunch accelerated by a wakefield are largely determined by the initial bunch dimensions. Present-day injectors are still incapable of ensuring the initial spatial parameters of the bunches required for their acceleration without increasing the energy spread of the bunch electrons. In connection with this, the possibility is studied of improving the energy characteristics of an accelerated bunch by precompressing it in the longitudinal direction in the stage of trapping by a wakefield. Analytic formulas are derived that describe the one-dimensional dynamics of the spatial and energy characteristics of a short (much shorter than the wakefield wavelength) electron bunch in both the trapping and acceleration stages. The analytical results obtained are shown to agree fairly well with the results from one-dimensional and three-dimensional simulations, provided that the electrons are injected into the region that is optimum for acceleration. The possibility is discussed of forming compressed bunches so as to ensure the high quality of the bunch in the course of its acceleration to high energies.     

The Ca2+-ATPase in Legume Root Nodule Peribacteroid Membrane as a Potential Key Determinant of Ca-Dependent Regulation of Symbiosome Functioning

Russian Journal of Plant Physiology - Certain aspects of Ca-dependent regulation of symbiosomes functioning mediated by the operation of Ca2+-translocating ATPase on the symbiosome membrane (SM)...     

Effect of SOS repair in enterobacteria on their interaction with the complement system

The interaction of E. coli (serovar 0124) and its rec A-mutants with serum complement resulting in the alternative pathway activation was studied. Bacteria VT1240 (original smooth strain), VT1241 (rough mutant) and VT 2240 (recA56 mutant) were shown to be complement-sensitive when treated with 1.5 X 10(8)--1.9 X 10(8) cells per ml of normal human serum, while the cells with SOS-activated system (recA441 mutant, strain VT3251) retained their viability. An alternative pathway of complement activation was minimal with E. coli VT1241, while VT3251 demonstrated intermediate activity. To decrease the level of complement components (AH50) and factor B (BH50) by 50%, 3.5 X 10(6)--4.5 X 10(6) cells of VT1240 and VT2240 strains were required. R-mutants and recA441 mutants caused a 50% reduction in AH50, when used in the amount of 6.4 X 10(7) and 2.6 X 10(7), respectively, the same degree of BH50 decrease was achieved with the amounts used equal to 1.1 X 10(8) and 4.3 X 10(6), respectively. C3 conversions caused by 4 X 10(8) cells in I ml of the normal human serum in the four strains tested accounted for 5-15%.     

In vitro activity of human translation initiation factor eIF4B is not affected by phosphomimetic amino acid substitutions S422D and S422E

Eukaryotic translation initiation factor eIF4B is necessary for ribosomal scanning through structured mRNA leaders. In higher eukaryotes, eIF4B serves as a downstream effector of several signaling pathways. In response to mitogenic stimuli, eIF4B undergoes multiple phosphorylations which are thought to regulate its activity. Recently, Ser422 was identified as a predominant site for human eIF4B phosphorylation via several signaling pathways, and phosphomimetic amino acid substitutions S422D or S422E were shown to activate eIF4B in living cells. However, stimulatory role of these modifications has never been analyzed directly. Here, using both mammalian reconstituted translation initiation assay and complete cell-free translation system, we perform a comparison of recombinant eIF4B derivatives with the wild type recombinant protein, and do not find any difference in their activities. On the contrary, native eIF4B purified from HeLa cells reveals significantly higher activity in both assays. Thus, the effects of S422D and S422E substitutions on eIF4B activity in living cells observed previously either require some other protein modification(s), or may only be manifested in an intact cell. Our study raises the question on whether the phosphorylation of Ser422 is sufficient for eIF4B activation observed upon mitogenic stimulation.     

Assessment of radiation exposure level for hydrobionts in some special industrial ponds at the "Mayak" PA

Evaluation of the radionuclide content in the ecosystem components (water, sediments, aquatic organisms) of industrial reservoirs-storages of liquid radioactive waste of the "Mayak" PA (reservoirs R-4, R-10, R-11, R-17, R-9) and the estimation of the absorbed dose rate in aquatic organisms of these reservoirs using the software package ERICA Assessment Tool 1.0 May 2009 have been performed. Gradient of the absorbed dose rate for the detected taxonomic groups of hydrobionts in the series of the studied reservoirs R-11 --> R-10 --> R-4 --> R-17 --> R-9 was almost equal to one order of magnitude. The estimated absorbed dose rate for phytoplankton ranged from 5.4 x 10(0) mGy/day (R-11) to 4.0 x 10(4) mGy/day (R-9), for zooplankton--from 6.4 x 10(-1) mGy/day (R-11) to 3.8 x 10(3) mGy/day (R-9), for zoobenthos (chironomids)--from 5.6 x 10(0) mGy/day (R-11) to 1.1 x 10(3) mGy/day (R-17), for fish (roach)--from 8.0 x 10(-1) mGy/day (R-11) to 1.9 x 10(1) mGy/day (R-4).     

Changes in expression of genes encoding antioxidant enzymes, heme oxygenase-1, Bcl-2, and Bcl-xl and in level of reactive oxygen species in tumor cells resistant to doxorubicin

The relationship between expression of genes encoding key antioxidant enzymes, heme oxygenase-1, Bcl-2, and Bcl-xl and change in production of reactive oxygen species (ROS) resulting from development of resistance of cancer cells K562, MCF-7, and SKOV-3 to the prooxidant chemotherapeutic agent doxorubicin (DOX) has been studied. Significant increase in mRNA level and activity of Mn-superoxide dismutase (Mn-SOD), catalase, and selenium-dependent glutathione peroxidase-1 (GPx-1) and reduced ROS level was found in resistant K562/DOX and SKVLB cells. In contrast, no change in ROS level was observed in MCF-7/DOX cells in parallel with decrease in Mn-SOD and catalase mRNAs and corresponding activities concurrently with high increase in GPx-1 mRNA and activity. As a result of the development of resistance, a similarity was found between the change in ROS level and the change in ho-1 and bcl-2 gene expression, whereas elevation of bcl-xl gene expression was observed in all three types of resistant cells. Particular features of development of adaptive antioxidant response as well as redox-dependent change in bcl-2 gene expression under formation of DOX resistance of cancer cells of different genesis are discussed.     

alphaCaMKII Is essential for cerebellar LTD and motor learning

Activation of postsynaptic alpha-calcium/calmodulin-dependent protein kinase II (alphaCaMKII) by calcium influx is a prerequisite for the induction of long-term potentiation (LTP) at most excitatory synapses in the hippocampus and cortex. Here we show that postsynaptic LTP is unaffected at parallel fiber-Purkinje cell synapses in the cerebellum of alphaCaMKII(-/-) mice. In contrast, a long-term depression (LTD) protocol resulted in only transient depression in juvenile alphaCaMKII(-/-) mutants and in robust potentiation in adult mutants. This suggests that the function of alphaCaMKII in parallel fiber-Purkinje cell plasticity is opposite to its function at excitatory hippocampal and cortical synapses. Furthermore, alphaCaMKII(-/-) mice showed impaired gain-increase adaptation of both the vestibular ocular reflex and optokinetic reflex. Since Purkinje cells are the only cells in the cerebellum that express alphaCaMKII, our data suggest that an impairment of parallel fiber LTD, while leaving LTP intact, is sufficient to disrupt this form of cerebellar learning.     

Efficient cap-dependent translation of mammalian mRNAs with long and highly structured 5′-untranslated regions in vitro and in vivo

According to the generally accepted scanning model proposed by M. Kozak, the secondary structure of the 5′-untranslated region (5′-UTR) of eukaryotic mRNA can only inhibit the translation initiation by counteracting migration of the 40S ribosomal subunit along the mRNA polynucleotide chain. The existence of efficiently translatable mRNAs with long and highly structured 5′-UTRs is incompatible with the cap-dependent scanning mechanism. Such mRNAs are expected to use alternative ways of translation initiation to be efficiently translated, primarily the mechanism of internal ribosome entry mediated by internal ribosome entry sites (IRESs), special RNA structures that reside in the 5′-UTR. The paper shows that this viewpoint is incorrect and is probably based on experiments with mRNA translation in rabbit reticulocyte lysate. This cell-free system fails to adequately reflect the relative translation efficiencies observed for different mRNAs in vivo. Five structurally similar mRNAs with either short leaders of the β-globin and β-actin mRNAs or long and highly structured 5′-UTRs of the c-myc, LINE-1, and Apaf-1 mRNAs displayed comparable translation activities in transfected cells and an entire cytoplasmic extract of cultivated cells. Translation activity proved to strongly depend on the presence of a cap at the 5′ end.