Controlling the Spin Polarization of the Electron Current in a Semimagnetic Resonant-Tunneling Diode

The spin filtering effect of the electron current in a double-barrier resonant-tunneling diode (RTD) consisting of ZnMnSe semimagnetic layers has been studied theoretically. The influence of the distribution of the magnesium ions on the coefficient of the spin polarization of the electron current has been investigated. The dependence of the spin filtering degree of the electron current on the external magnetic field and the bias voltage has been obtained. The effect of the total spin polarization of the electron current has been predicted. This effect is characterized by total suppression of the spin-up component of electron current, that takes place when the Fermi level coincides with the lowest Landau level for spin-up electrons in the RTD semimagnetic emitter

Behavior of the emission from atomic oxygen of the atmosphere at 557.7 nm during the events of stratospheric warming over East Siberia

The influence of stratospheric warming on the atomic oxygen emission at 557.7-nm wavelength (airglow) was investigated based on data obtained at the Geophysical Observatory of ISTP SB RAS (52°N, 103°E) in [1997][1998][1999][2000][2001][2002][2003][2004][2005]. In this period, several cases of anomalous behavior of the 557.7-nm emission intensity in the absence of strong geomagnetic disturbances have been recorded. It has been found that these cases of the growth of intensity of atmospheric emission at 557.7 nm in the height region of the mesosphere and lower thermosphere, have been caused by strong stratospheric warming when the disturbance covers a wide range of atmospheric altitudes. It should be emphasized that high concentration of centers of stratospheric warming is characteristic of Asia and, in particular, of the East Siberia that can result in the formation of regional peculiarities in characteristics of the airglow

Cytosine-to-Uracil Deamination by SssI DNA Methyltransferase

The prokaryotic DNA(cytosine-5)methyltransferase M.SssI shares the specificity of eukaryotic DNA methyltransferases (CG) and is an important model and experimental tool in the study of eukaryotic DNA methylation. Previously, M.SssI was shown to be able to catalyze deamination of the target cytosine to uracil if the methyl donor S-adenosyl-methionine (SAM) was missing from the reaction. To test whether this side-activity of the enzyme can be used to distinguish between unmethylated and C5-methylated cytosines in CG dinucleotides, we re-investigated, using a sensitive genetic reversion assay, the cytosine deaminase activity of M.SssI. Confirming previous results we showed that M.SssI can deaminate cytosine to uracil in a slow reaction in the absence of SAM and that the rate of this reaction can be increased by the SAM analogue 5’-amino-5’-deoxyadenosine. We could not detect M.SssI-catalyzed deamination of C5-methylcytosine (m5C). We found conditions where the rate of M.SssI mediated C-to-U deamination was at least 100-fold higher than the rate of m5C-to-T conversion. Although this difference in reactivities suggests that the enzyme could be used to identify C5-methylated cytosines in the epigenetically important CG dinucleotides, the rate of M.SssI mediated cytosine deamination is too low to become an enzymatic alternative to the bisulfite reaction. Amino acid replacements in the presumed SAM binding pocket of M.SssI (F17S and G19D) resulted in greatly reduced methyltransferase activity. The G19D variant showed cytosine deaminase activity in E. coli, at physiological SAM concentrations. Interestingly, the C-to-U deaminase activity was also detectable in an E. coli ung+ host proficient in uracil excision repair

Comprehensive analysis of the base composition around the transcription start site in Metazoa

BACKGROUND: The transcription start site of a metazoan gene remains poorly understood, mostly because there is no clear signal present in all genes. Now that several sequenced metazoan genomes have been annotated, we have been able to compare the base composition around the transcription start site for all annotated genes across multiple genomes. RESULTS: The most prominent feature in the base compositions is a significant local variation in G+C content over a large region around the transcription start site. The change is present in all animal phyla but the extent of variation is different between distinct classes of vertebrates, and the shape of the variation is completely different between vertebrates and arthropods. Furthermore, the height of the variation correlates with CpG frequencies in vertebrates but not in invertebrates and it also correlates with gene expression, especially in mammals. We also detect GC and AT skews in all clades (where %G is not equal to %C or %A is not equal to %T respectively) but these occur in a more confined region around the transcription start site and in the coding region. CONCLUSIONS: The dramatic changes in nucleotide composition in humans are a consequence of CpG nucleotide frequencies and of gene expression, the changes in Fugu could point to primordial CpG islands, and the changes in the fly are of a totally different kind and unrelated to dinucleotide frequencies

A scenario of pulsed ecrh wall conditioning in hydrogen for the Wendelstein 7-X helias

A new wall conditioning scenario in hydrogen atmosphere for the Wendelstein 7-X stellarator-helias (W7-X) has been proposed and tested in part. Feasibility of the proposed scenario has been demonstrated on W7-X at OP1.2b experimental campaign during investigation of a chain of ultra-short pulsed electron cyclotron resonance heating plasma discharges.Був запропонований і випробуваний новий сценарій кондиціонування стінки в атмосфері водню для стеларатора-хеліаса Wendelstein 7-X (W7-X). Застосовано принцип кондиціонування стінок камери атомарним воднем, виробленим в плазмі, який хімічно взаємодіє з домішками, адсорбованими на поверхні камери, зверненої до плазми. Можливість реалізації запропонованого сценарію було підтверджено на W7-X під час експериментальної кампанії OP1.2b при дослідженні ланцюжка ультракоротких імпульсів з нагріванням за допомогою електронного циклотронного резонансу.Был предложен и испытан новый сценарий кондиционирования стенки в атмосфере водорода для стелларатора-хелиаса Wendelstein 7-X (W7-X). Использован принцип кондиционирования стенок камеры атомарным водородом, производимым в плазме, который химически взаимодействует с примесями, адсорбированными на поверхности камеры, обращенной к плазме. Возможность реализации предложенного сценария была подтверждена на W7-X во время экспериментальной кампании OP1.2b при изучении цепочки ультракоротких импульсов в плазме с нагревом в условиях электронного циклотронного резонанса

Insights into corn genes derived from large-scale cDNA sequencing

We present a large portion of the transcriptome of Zea mays, including ESTs representing 484,032 cDNA clones from 53 libraries and 36,565 fully sequenced cDNA clones, out of which 31,552 clones are non-redundant. These and other previously sequenced transcripts have been aligned with available genome sequences and have provided new insights into the characteristics of gene structures and promoters within this major crop species. We found that although the average number of introns per gene is about the same in corn and Arabidopsis, corn genes have more alternatively spliced isoforms. Examination of the nucleotide composition of coding regions reveals that corn genes, as well as genes of other Poaceae (Grass family), can be divided into two classes according to the GC content at the third position in the amino acid encoding codons. Many of the transcripts that have lower GC content at the third position have dicot homologs but the high GC content transcripts tend to be more specific to the grasses. The high GC content class is also enriched with intronless genes. Together this suggests that an identifiable class of genes in plants is associated with the Poaceae divergence. Furthermore, because many of these genes appear to be derived from ancestral genes that do not contain introns, this evolutionary divergence may be the result of horizontal gene transfer from species not only with different codon usage but possibly that did not have introns, perhaps outside of the plant kingdom. By comparing the cDNAs described herein with the non-redundant set of corn mRNAs in GenBank, we estimate that there are about 50,000 different protein coding genes in Zea. All of the sequence data from this study have been submitted to DDBJ/GenBank/EMBL under accession numbers EU940701–EU977132 (FLI cDNA) and FK944382-FL482108 (EST)

Astrocytes mediate synapse elimination through MEGF10 and MERTK pathways

To achieve its precise neural connectivity, the developing mammalian nervous system undergoes extensive activity-dependent synapse remodeling. Recently microglial cells have been shown to be responsible for a portion of synaptic remodeling, but the remaining mechanisms remain mysterious. Here we report a new role for astrocytes in actively engulfing CNS synapses. This process helps to mediate synapse elimination, requires the Megf10 and Mertk phagocytic pathways, and is strongly dependent on neuronal activity. Developing mice deficient in both astrocyte pathways fail to normally refine their retinogeniculate connections and retain excess functional synapses. Lastly, we show that in the adult mouse brain, astrocytes continuously engulf both excitatory and inhibitory synapses. These studies reveal a novel role for astrocytes in mediating synapse elimination in the developing and adult brain, identify Megf10 and Mertk as critical players in the synapse remodeling underlying neural circuit refinement, and have important implications for understanding learning and memory as well as neurological disease processes

Nucleotide and phylogenetic analyses of the Chlamydia trachomatis ompA gene indicates it is a hotspot for mutation

<p>Abstract</p> <p>Background</p> <p>Serovars of the human pathogen <it>Chlamydia trachomatis </it>occupy one of three specific tissue niches. Genomic analyses indicate that the serovars have a phylogeny congruent with their pathobiology and have an average substitution rate of less than one nucleotide per kilobase. In contrast, the gene that determines serovar specificity, <it>ompA</it>, has a phylogenetic association that is not congruent with tissue tropism and has a degree of nucleotide variability much higher than other genomic loci. The <it>ompA </it>gene encodes the major surface-exposed antigenic determinant, and the observed nucleotide diversity at the <it>ompA </it>locus is thought to be due to recombination and host immune selection pressure. The possible contribution of a localized increase in mutation rate, however, has not been investigated.</p> <p>Results</p> <p>Nucleotide diversity and phylogenetic relationships of the five constant and four variable domains of the <it>ompA </it>gene, as well as several loci surrounding <it>ompA</it>, were examined for each serovar. The loci flanking the <it>ompA </it>gene demonstrated that nucleotide diversity increased monotonically as <it>ompA </it>is approached and that their gene trees are not congruent with either <it>ompA </it>or tissue tropism. The variable domains of the <it>ompA </it>gene had a very high level of non-synonymous change, which is expected as these regions encode the surface-exposed epitopes and are under positive selection. However, the synonymous changes are clustered in the variable regions compared to the constant domains; if hitchhiking were to account for the increase in synonymous changes, these substitutions should be more evenly distributed across the gene. Recombination also cannot entirely account for this increase as the phylogenetic relationships of the constant and variable domains are congruent with each other.</p> <p>Conclusions</p> <p>The high number of synonymous substitutions observed within the variable domains of <it>ompA </it>appears to be due to an increased mutation rate within this region of the genome, whereas the increase in nucleotide substitution rate and the lack of phylogenetic congruence in the regions flanking <it>ompA </it>are characteristic motifs of gene conversion. Together, the increased mutation rate in the <it>ompA </it>gene, in conjunction with gene conversion and positive selection, results in a high degree of variability that promotes host immune evasion.</p