Alignment Dynamics of Single-Walled Carbon Nanotubes in Pulsed Ultrahigh Magnetic Fields

We have measured the dynamic alignment properties of single-walled carbon nanotube (SWNT) suspensions in pulsed high magnetic fields through linear dichroism spectroscopy. Millisecond-duration pulsed high magnetic fields up to 56 T as well as microsecond-duration pulsed ultrahigh magnetic fields up to 166 T were used. Due to their anisotropic magnetic properties, SWNTs align in an applied magnetic field, and because of their anisotropic optical properties, aligned SWNTs show linear dichroism. The characteristics of their overall alignment depend on several factors, including the viscosity and temperature of the suspending solvent, the degree of anisotropy of nanotube magnetic susceptibilities, the nanotube length distribution, the degree of nanotube bundling, and the strength and duration of the applied magnetic field. In order to explain our data, we have developed a theoretical model based on the Smoluchowski equation for rigid rods that accurately reproduces the salient features of the experimental data.Comment: 20 pages, 6 figure

Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Ballistic spin polarized transport through diluted magnetic semiconductor (DMS) single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field are varied. An interesting beat pattern in the TMR and spin polarization is found for different NMS/DMS double barrier structures which arises from an interplay between the spin-up and spin-down electron channels which are splitted by the s-d exchange interaction.Comment: 4 pages, 6 figures, submitted to Phys. Rev.

Longitudinal spin transport in diluted magnetic semiconductor superlattices: the effect of the giant Zeeman splitting

Longitudinal spin transport in diluted magnetic semiconductor superlattices is investigated theoretically. The longitudinal magnetoconductivity (MC) in such systems exhibits an oscillating behavior as function of an external magnetic field. In the weak magnetic field region the giant Zeeman splitting plays a dominant role which leads to a large negative magnetoconductivity. In the strong magnetic field region the MC exhibits deep dips with increasing magnetic field. The oscillating behavior is attributed to the interplay between the discrete Landau levels and the Fermi surface. The decrease of the MC at low magnetic field is caused by the $s-d$ exchange interaction between the electron in the conduction band and the magnetic ions.Comment: 6 pages, 9 figures, submitted to Phys. Rev.

Recombination Phenotypes of Escherichia coli greA Mutants

<p>Abstract</p> <p>Background</p> <p>The elongation factor GreA binds to RNA polymerase and modulates transcriptional pausing. Some recent research suggests that the primary role of GreA may not be to regulate gene expression, but rather, to promote the progression of replication forks which collide with RNA polymerase, and which might otherwise collapse. Replication fork collapse is known to generate dsDNA breaks, which can be recombinogenic. It follows that GreA malfunction could have consequences affecting homologous recombination.</p> <p>Results</p> <p><it>Escherichia coli </it>mutants bearing substitutions of the active site acidic residues of the transcription elongation factor GreA, D41N and E44K, were isolated as suppressors of growth inhibition by a toxic variant of the bacteriophage lambda Red-beta recombination protein. These mutants, as well as a D41A <it>greA </it>mutant and a <it>greA </it>deletion, were tested for proficiency in recombination events. The mutations were found to increase the efficiency of RecA-RecBCD-mediated and RecA-Red-mediated recombination, which are replication-independent, and to decrease the efficiency of replication-dependent Red-mediated recombination.</p> <p>Conclusion</p> <p>These observations provide new evidence for a role of GreA in resolving conflicts between replication and transcription.</p

Depletion of Plasmodium berghei Plasmoredoxin Reveals a Non-Essential Role for Life Cycle Progression of the Malaria Parasite

Proliferation of the pathogenic Plasmodium asexual blood stages in host erythrocytes requires an exquisite capacity to protect the malaria parasite against oxidative stress. This function is achieved by a complex antioxidant defence system composed of redox-active proteins and low MW antioxidants. Here, we disrupted the P. berghei plasmoredoxin gene that encodes a parasite-specific 22 kDa member of the thioredoxin superfamily. The successful generation of plasmoredoxin knockout mutants in the rodent model malaria parasite and phenotypic analysis during life cycle progression revealed a non-vital role in vivo. Our findings suggest that plasmoredoxin fulfils a specialized and dispensable role for Plasmodium and highlights the need for target validation to inform drug development strategies

A Reduction in Ribonucleotide Reductase Activity Slows Down the Chromosome Replication Fork but Does Not Change Its Localization

BACKGROUND:It has been proposed that the enzymes of nucleotide biosynthesis may be compartmentalized or concentrated in a structure affecting the organization of newly replicated DNA. Here we have investigated the effect of changes in ribonucleotide reductase (RNR) activity on chromosome replication and organization of replication forks in Escherichia coli. METHODOLOGY/PRINCIPAL FINDINGS:Reduced concentrations of deoxyribonucleotides (dNTPs) obtained by reducing the activity of wild type RNR by treatment with hydroxyurea or by mutation, resulted in a lengthening of the replication period. The replication fork speed was found to be gradually reduced proportionately to moderate reductions in nucleotide availability. Cells with highly extended C periods showed a "delay" in cell division i.e. had a higher cell mass. Visualization of SeqA structures by immunofluorescence indicated no change in organization of the new DNA upon moderate limitation of RNR activity. Severe nucleotide limitation led to replication fork stalling and reversal. Well defined SeqA structures were not found in situations of extensive replication fork repair. In cells with stalled forks obtained by UV irradiation, considerable DNA compaction was observed, possibly indicating a reorganization of the DNA into a "repair structure" during the initial phase of the SOS response. CONCLUSION/SIGNIFICANCE:The results indicate that the replication fork is slowed down in a controlled manner during moderate nucleotide depletion and that a change in the activity of RNR does not lead to a change in the organization of newly replicated DNA. Control of cell division but not control of initiation was affected by the changes in replication elongation

Characteristic of bacteriurii in patients with urinary infections, living in different regions

The aim of the research is to give comparative characteristics of bacteriurii and microflora sensitiveness to antibiotics in persons suffering from urinary infections (two regions, Moscow and Tyumen) Material and methods of research: 173 patients with urinary infection (cystitis, pyelonephritis) were examined. Material for research was media portion of freely produced urine.The investigation of bacteriurii was carried out with quantitative method according to recommendations of National Committee on Clinic Laboratory Standards (NCCLS, USA) The results obtained and discussion It is shown that E. coli and Enterococus were most frequently in persons living in Tyumen. E. Coli and K. pneumomiae were revealed in Moscow. The most active preparation against E. coli Tyumen inhabitants were nitrofuranam, karbopenemy, cefalosporiny of III generation and less important aminoglikozidy, against Enterococcus — ftorkhinoly, vancomicin, Laevomycetin. In patients with infections urinary infections in Moscow the most active preparations against E. coli and К pneumomiae were Karbopenemy, aminoglikozidy and cefalosporiny of III generation and ftorkhinoly. High resistance to Nitrofuranam was marked (= 62 percents). Conclusion. Bacteriuriii features were revealed in patients with the urinary infections ways in different regions of the Russian Federation. The most active preparations which can be used for the treatment of patients with urinary infections taking into account the exciters given were shown on resistance.Цель работы — дать сравнительную характеристику бактерийурии и чувствительности микрофлоры к антибиотикам у жителей двух регионов (г. Москва и г. Тюмень), страдающих инфекциями мочевыводящих путей. Материал и методы исследования: всего обследовано 173 больных с инфекцией мочевыводящих путей (цистит, пиелонефрит). Материалом для исследования была средняя порция свободно выпущенной мочи. Исследование бактерийурии проводилось количественным методом согласно рекомендациям Национального комитета по клиническим лабораторным стандартам (NCCLS, США). Полученные результаты и обсуждение. Показано, что у жителей г. Тюмени наиболее часто выделяются из мочи E.Coli и Enterococcus, а в г. Москве — Е. Coli и К. pneumoniae. Наиболее активными препаратами в отношении Е. СоМ у больных в г. Тюмени являлись нитрофураны, карбопенемы, цефалоспорины III поколения и, в меньшей степени, аминогликозиды; в отношении Enterococcus — фторхинолоны, ванкомицин и левомицетин (хлорамфеникол). У больных с инфекцией мочевыводящих путей в г. Москве наиболее активными препаратами в отношении Е. Coli и К. pneumoniae оказались карбопенемы, аминогликозиды и цефалоспорины III поколения, а также фторхинолоны. При этом к нитрофуранам в случае выделения К. pneumoniae отмечалась высокая резистентность (почти 62%). Заключение. Проведенные исследования выявили особенности бактерийурии у больных с инфекциями мочевыводящих путей в различных регионах РФ, а также показали наиболее активные препараты, которые могут быть использованы для лечения больных с учетом данных по локальной резистентности возбудителей

Regulation of Cancer Aggressive Features in Melanoma Cells by MicroRNAs

MicroRNAs (miRNAs) are small non-coding RNAs with regulatory roles, which are involved in a broad spectrum of physiological and pathological processes, including cancer. A common strategy for identification of miRNAs involved in cell transformation is to compare malignant cells to normal cells. Here we focus on identification of miRNAs that regulate the aggressive phenotype of melanoma cells. To avoid differences due to genetic background, a comparative high-throughput miRNA profiling was performed on two isogenic human melanoma cell lines that display major differences in their net proliferation, invasion and tube formation activities. This screening revealed two major cohorts of differentially expressed miRNAs. We speculated that miRNAs up-regulated in the more-aggressive cell line contribute oncogenic features, while the down-regulated miRNAs are tumor suppressive. This assumption was further tested experimentally on five candidate tumor suppressive miRNAs (miR-31, -34a, -184, -185 and -204) and on one candidate oncogenic miRNA (miR-17-5p), all of which have never been reported before in cutaneous melanoma. Remarkably, all candidate Suppressive-miRNAs inhibited net proliferation, invasion or tube formation, while miR-17-5p enhanced cell proliferation. miR-34a and miR-185 were further shown to inhibit the growth of melanoma xenografts when implanted in SCID-NOD mice. Finally, all six candidate miRNAs were detected in 15 different metastatic melanoma specimens, attesting for the physiological relevance of our findings. Collectively, these findings may prove instrumental for understanding mechanisms of disease and for development of novel therapeutic and staging technologies for melanoma