163 research outputs found
Sequence and mutational analysis of the devBCA gene cluster encoding a putative ABC transporter in the cyanobacterium Anabaena variabilis ATCC 29413
AbstractThe devBCA gene cluster (dev for development), shown to be essential for envelope formation in heterocysts of Anabaena sp. strain PCC 7120, was identified in the gene bank of a second heterocyst-forming strain, Anabaena variabilis ATCC 29413. Sequence and structural organization of the three genes, encoding subunits of a presumptive ABC transporter, were nearly identical in both strains. Mutants of A. variabilis defective in the devA gene were constructed. As devA mutants of Anabaena 7120, A. variabilis mutants were unable to grow on N2 as sole nitrogen source due to incomplete differentiation of heterocysts
Approximate Hermitian-Yang-Mills structures and semistability for Higgs bundles. II: Higgs sheaves and admissible structures
We study the basic properties of Higgs sheaves over compact K\"ahler
manifolds and we establish some results concerning the notion of semistability;
in particular, we show that any extension of semistable Higgs sheaves with
equal slopes is semistable. Then, we use the flattening theorem to construct a
regularization of any torsion-free Higgs sheaf and we show that it is in fact a
Higgs bundle. Using this, we prove that any Hermitian metric on a
regularization of a torsion-free Higgs sheaf induces an admissible structure on
the Higgs sheaf. Finally, using admissible structures we proved some properties
of semistable Higgs sheaves.Comment: 18 pages; some typos correcte
Septal Junctions in Filamentous Heterocyst-Forming Cyanobacteria
In the filaments of heterocyst-forming cyanobacteria, septal junctions that traverse the septal peptidoglycan join adjacent cells, allowing intercellular communication. Perforations in the septal peptidoglycan have been observed, and proteins involved in the formation of such perforations and putative protein components of the septal junctions have been identified, but their relationships are debatedEspaña, Plan Nacional de Investigaci´601027022on BFU2014 - 56757 - P (EF) and BFU2013 - 157 44686 -
Hydroxide in olivine: A quantitative determination of the absolute amount and calibration of the IR spectrum
Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by ^(15)N nuclear reaction analysis and used the results to calibrate the common infrared (IR) spectroscopic method for quantitative hydrogen analysis of olivine. OH content (expressed as parts per million H_2O by weight) is 0.188 times the total integrated absorbance of the fundamental OH stretching bands in the 3750–3100 cm^(−1) region. The results indicate that an upward revision of some previous determinations by factors of between 2 and 4 is necessary. The most hydrous naturally occurring mantle-derived olivine analyzed to date contains 240 ppm wt. H_2O. Retrospective application of this calibration to experimentally hydrated olivines may be limited by spectral differences in some cases and by the previous use of nonpolarized IR spectra
Human endogenous retrovirus HERV-K(HML-2) encodes a stable signal peptide with biological properties distinct from Rec
<p>Abstract</p> <p>Background</p> <p>The human endogenous retrovirus HERV-K(HML-2) family is associated with testicular germ cell tumors (GCT). Various HML-2 proviruses encode viral proteins such as Env and Rec.</p> <p>Results</p> <p>We describe here that HML-2 Env gives rise to a 13 kDa signal peptide (SP) that harbors a different C-terminus compared to Rec. Subsequent to guiding Env to the endoplasmatic reticulum (ER), HML-2 SP is released into the cytosol. Biochemical analysis and confocal microscopy demonstrated that similar to Rec, SP efficiently translocates to the granular component of nucleoli. Unlike Rec, SP does not shuttle between nucleus and cytoplasm. SP is less stable than Rec as it is subjected to proteasomal degradation. Moreover, SP lacks export activity towards HML-2 genomic RNA, the main function of Rec in the original viral context, and SP does not interfere with Rec's RNA export activity.</p> <p>Conclusion</p> <p>SP is a previously unrecognized HML-2 protein that, besides targeting and translocation of Env into the ER lumen, may exert biological functions distinct from Rec. HML-2 SP represents another functional similarity with the closely related Mouse Mammary Tumor Virus that encodes an Env-derived SP named p14. Our findings furthermore support the emerging concept of bioactive SPs as a conserved retroviral strategy to modulate their host cell environment, evidenced here by a "retroviral fossil". While the specific role of HML-2 SP remains to be elucidated in the context of human biology, we speculate that it may be involved in immune evasion of GCT cells or tumorigenesis.</p
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Practical IR extinction coefficients for water in commercial glasses determined by nuclear reaction analysis
For a number of commercial glasses with different chemical compositions the water contents were determined by nuclear reaction analysis (NRA) measurements. These results were used to deduce practical extinction coefficients by comparison with the measured IR absorbance values at 2.8 μm. For aluminosilicate and television glasses the practical molar extinction coefficients are given for the first time. Practical extinction coefficients are dependent upon glass composition. With increasing basicity of the glasses studied they decrease from 182 to 24 l/(mol cm)
Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
D.J.N. was supported by a Queen Mary University of London College studentship. M.N.M. was the recipient of an FPU (Formación del Personal Universitario) fellowship from the Spanish Government. Work in Seville was supported by grant BFU2011-22762 from Plan Nacional de Investigación, Spain, cofinanced by the European Regional Development Fund, and by Plan Andaluz de Investigación, Regional Government of AndalucÃa (grant P10-CVI-6665). Research in Tübingen was supported by the Deutsche Forschungsgemeinschaft (SFB766)
Systematic Assessment of Blood-Borne MicroRNAs Highlights Molecular Profiles of Endurance Sport and Carbohydrate Uptake
Multiple studies endorsed the positive effect of regular exercise on mental and physical
health. However, the molecular mechanisms underlying training-induced fitness in combination
with personal life-style remain largely unexplored. Circulating biomarkers such as microRNAs
(miRNAs) offer themselves for studying systemic and cellular changes since they can be collected
from the bloodstream in a low-invasive manner. In Homo sapiens miRNAs are known to regulate a
substantial number of protein-coding genes in a post-transcriptional manner and hence are of great
interest to understand differential gene expression profiles, offering a cost-effective mechanism to
study molecular training adaption, and connecting the dots from genomics to observed phenotypes.
Here, we investigated molecular expression patterns of 2549 miRNAs in whole-blood samples from
23 healthy and untrained adult participants of a cross-over study, consisting of eight weeks of
endurance training, with several sessions per week, followed by 8 weeks of washout and another
8 weeks of running, using microarrays. Participants were randomly assigned to one of the two
study groups, one of which administered carbohydrates before each session in the first training
period, and switching the treatment group for the second training period. During running sessions
clinical parameters as heartbeat frequency were recorded. This information was extended with
four measurements of maximum oxygen uptake (VO2 max) for each participant. We observed that
multiple circulating miRNAs show expression changes after endurance training, leveraging the
capability to separate the blood samples by training status. To this end, we demonstrate that most
of the variance in miRNA expression can be explained by both common and known biological
and technical factors. Our findings highlight six distinct clusters of miRNAs, each exhibiting an
oscillating expression profile across the four study timepoints, that can effectively be utilized to
predict phenotypic VO2 max levels. In addition, we identified miR-532-5p as a candidate marker to
determine personal alterations in physical training performance on a case-by-case analysis taking
the influence of a carbohydrate-rich nutrition into account. In literature, miR-532-5p is known
as a common down-regulated miRNA in diabetes and obesity, possibly providing a molecular link between cellular homeostasis, personal fitness levels, and health in aging. We conclude that
circulating miRNA expression can be altered due to regular endurance training, independent of the
carbohydrate (CHO) availability in the training timeframe. Further validation studies are required
to confirm the role of exercise-affected miRNAs and the extraordinary function of miR-532-5p in
modulating the metabolic response to a high availability of glucose
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