Experimental study of photon beam polarimeter based on nuclear e+e- pair production in an amorphous target

The experimental method of the linearly polarized photons polarimetry,using incoherent e+e- pair production process has been investigated on the beam of coherent bremsstrahlung (CB) photons in the energy range of 0.9-1.1 GeV at the Yerevan synchrotron.Comment: 6 pages (text),10 figure

Measurement of the Cross Section Asymmetry of the Reaction gp-->pi0p in the Resonance Energy Region Eg = 0.5 - 1.1 GeV

The cross section asymmetry Sigma has been measured for the photoproduction of pi0-mesons off protons, using polarized photons in the energy range Eg = 0.5 - 1.1 GeV. The CM angular coverage is Theta = 85 - 125 deg with energy and angle steps of 25 MeV and 5 deg, respectively. The obtained Sigma data, which cover the second and third resonance regions, are compared with existing experimental data and recent phenomenological analyses. The influence of these measurements on such analyses is also considered

Prothymosin α fragmentation in apoptosis

AbstractWe observed fragmentation of an essential proliferation-related human nuclear protein prothymosin α in the course of apoptosis induced by various stimuli. Prothymosin α cleavage occurred at the DDVD99 motif. In vitro, prothymosin α could be cleaved at D99 by caspase-3 and -7. Caspase hydrolysis disrupted the nuclear localization signal of prothymosin α and abrogated the ability of the truncated protein to accumulate inside the nucleus. Prothymosin α fragmentation may therefore be proposed to disable intranuclear proliferation-related function of prothymosin α in two ways: by cleaving off a short peptide containing important determinants, and by preventing active nuclear uptake of the truncated protein

Early Alteration of Nucleocytoplasmic Traffic Induced by Some RNA Viruses

AbstractA HeLa cell line expressing the green fluorescent protein fused to the SV40 T-antigen nuclear localization signal (EGFP-NLS) was established. Fluorescence in these cells was confined to the nuclei. After poliovirus infection, cytoplasmic fluorescence in a proportion of cells could be detected by 1 h postinfection (p.i.) and in virtually all of the fluorescent cells by 2 h p.i. The relocation could be prevented by cycloheximide but not by inhibition of poliovirus replication by guanidine · HCl. Nuclear exit of a protein composed of three copies of GFP fused to the NLS also occurred upon poliovirus infection. A similar redistribution of EGFP-NLS took place upon infection with coxsakievirus B3 and, to a lesser extent, with vesicular stomatitis virus. The EGFP-NLS efflux was not due to the loss of NLS. Thus, some positive-strand and negative-strand RNA viruses trigger a rapid nonspecific relocation of nuclear proteins

Arabidopsis thaliana phytaspase: identification and peculiar properties

Phytaspases are plant cell death-related proteases of the subtilisin-like protease family that possess an unusual aspartate cleavage specificity. Although phytaspase activity is widespread in plants, phytaspase of Arabidopsis thaliana (L.) Heynh. has escaped detection and identification thus far. Here, we show that a single gene (At4 g10540) out of 56 A. thaliana subtilisin-like protease genes encodes a phytaspase. The recombinant phytaspase was overproduced in Nicotiana benthamiana Domin leaves, isolated, and its substrate specificity and properties were characterised. At pH 5.5, at physiological mildly acidic reaction conditions, the Arabidopsis phytaspase was shown to be strictly Asp-specific. The strongly preferred cleavage motifs of the enzyme out of a panel of synthetic peptide substrates were YVAD and IETD, while the VEID-based substrate preferred by the tobacco and rice phytaspases was almost completely resistant to hydrolysis. At neutral pH, however, the Arabidopsis phytaspase could hydrolyse peptide substrates after two additional amino acid residues, His and Phe, in addition to Asp. This observation may indicate that the repertoire of Arabidopsis phytaspase targets could possibly be regulated by the conditions of the cellular environment. Similar to tobacco and rice phytaspases, the Arabidopsis enzyme was shown to accumulate in the apoplast of epidermal leaf cells. However, in stomatal cells Arabidopsis phytaspase was observed inside the cells, possibly co-localising with vacuole. Our study thus demonstrates that the Arabidopsis phytaspase possesses both important similarities with and distinctions from the already known phytaspases, and is likely to be the most divergent member of the phytaspase family

From structure to function – a family portrait of plant subtilases

Subtilases (SBTs) are serine peptidases that are found in all three domains of life. As compared with homologs in other Eucarya, plant SBTs are more closely related to archaeal and bacterial SBTs, with which they share many biochemical and structural features. However, in the course of evolution, functional diversification led to the acquisition of novel, plant-specific functions, resulting in the present-day complexity of the plant SBT family. SBTs are much more numerous in plants than in any other organism, and include enzymes involved in general proteolysis as well as highly specific processing proteases. Most SBTs are targeted to the cell wall, where they contribute to the control of growth and development by regulating the properties of the cell wall and the activity of extracellular signaling molecules. Plant SBTs affect all stages of the life cycle as they contribute to embryogenesis, seed development and germination, cuticle formation and epidermal patterning, vascular development, programmed cell death, organ abscission, senescence, and plant responses to their biotic and abiotic environments. In this article we provide a comprehensive picture of SBT structure and function in plants.Instituto de Fisiología Vegeta

Search for right-handed W bosons in top quark decay

We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This measurement is consistent with the standard model prediction of f+=3.6x10^-4.Comment: Submitted to Physical Review D Rapid Communications 7 pages, 3 figure