Double-stranded DNA-packaging in icosahedral bacteriophages is believed to be driven by a packaging “machine” constituted by the portal protein and the two packaging/terminase proteins assembled at ...the unique portal vertex of the empty prohead shell. Although ATP hydrolysis is evidently the principal driving force, which component of the packaging machinery functions as the translocating ATPase has not been elucidated. Evidence suggests that the large packaging subunit is a strong candidate for the translocating ATPase. We have constructed new phage T4 terminase recombinants under the control of phage T7 promoter and overexpressed the packaging/terminase proteins gp16 and gp17 in various configurations. The hexahistidine-tagged-packaging proteins were purified to near homogeneity by Ni2+-agarose chromatography and were shown to be highly active for packaging DNA in vitro. The large packaging subunit gp17 but not the small subunit gp16 exhibited an ATPase activity. Although gp16 lacked ATPase activity, it enhanced the gp17-associated ATPase activity by >50-fold. The gp16 enhancement was specific and was due to an increased catalytic rate for ATP hydrolysis. A phosphorylated gp17 was demonstrated under conditions of low catalytic rates but not under high catalytic rates in the presence of gp16. The data are consistent with the hypothesis that a weak ATPase is transformed into a translocating ATPase of high catalytic capacity after assembly of the packaging machine.
First experience and results from the HERA- B vertex detector system Bauer, C.; Baumann, I.; Bräuer, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1998, Letnik:
418, Številka:
1
Journal Article
Recenzirano
The HERA-
B collaboration is building a detector to realize the ambitious goal of observing CP violation in decays of neutral B-mesons. A central element of the apparatus is the silicon vertex ...detector used to selectively trigger on these decays in a high charged particle multiplicity background environment and to reconstruct secondary vertices from such decays with high precision. The vertex detector, the supporting infrastructure and first results using prototype detectors are described. Results include imaging of the proton interaction region on the HERA-
B target, hit distributions in the detector planes, and alignment of the detectors with each other and the target.
The Cosmic Ray Tracking (CRT) detector system Bernlöhr, K.; Gamp, S.; Hermann, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/1996, Letnik:
369, Številka:
1
Journal Article
Recenzirano
The Cosmic Ray Tracking (CRT) project represents a study on the use of tracking detectors of the time projection chamber type to detect secondary cosmic ray particles in extensive air showers. In ...reconstructing the arrival direction of the primary cosmic ray particles, the CRT detectors take advantage of the angular correlation of secondary particles with the cosmic rays leading to these air showers.
In this paper, the detector hardware including the custom-designed electronics system is described in detail. A CRT detector module provides an active area of 2.5 m
2 and allows to measure track directions with a precision of 0.4°. It consists of two circular drift chambers of 1.8 m diameter with six sense wires each, and a 10cm thick iron plate between the two chambers. Each detector has a local electronics box with a readout, trigger, and monitoring system.
The detectors can distinguish penetrating muons from other types of charged secondaries. A large detector array could be used to search for
γ-ray point sources at energies above several TeV and for studies of the cosmic-ray composition. Ten detectors are in operation at the site of the HEGRA air shower array.
The cosmic ray tracking (CRT) detectors consist of two drift chambers of the TPC type and an iron plate as a muon filter between the two chambers. CRT detectors are designed to detect and identify ...secondary cosmic ray particles in extensive air showers. Each detector has a local electronics box with a readout, trigger, and monitoring system. The local computers at the detector stations are used for hit and track finding in parallel to the detector readout. Detector stations are permanently calibrated online, using the cosmic ray data. The online software, including data processing and calibration procedures, are presented in this paper.
Ten detectors are in operation at the site of the HEGRA air shower array. The detector performance has been evaluated using data from these detectors and the HEGRA array as well as by Monte Carlo simulations. The spatial resolution has been found to be about 1 mm both in drift and in wire direction. The corresponding angular resolution is about 0.4° in each projection for a single track. Muons are usually identified if scattered by less than 2.5° in the iron plate, corresponding to energies above about 1 GeV. In HEGRA-triggered showers an overall muon identification efficiency of 87% is achieved, with a fraction of only 0.07% of the electrons being misidentified as muons.
Using the HERA-B detector, the b (b) over bar production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The b (b) over bar production was tagged via ...inclusive bottom quark decays into J/psi by exploiting the longitudinal separation of J/psi --> l(+)l(-) decay vertices from the primary proton-nucleus interaction. Both e(+)e(-) and mu(+)mu(-) channels have been reconstructed and the combined analysis yields the cross section sigma(b (b) over bar) = 32(-12)(+14)(stat) (+6)(-7)(sys) nb/nucleon.
Bacteriophage T4 and other double-stranded DNA-containing bacteriophages package DNA by the classical headful packaging mechanism. In this mechanism, the packaging machinery cuts a DNA concatemer and ...packages a single unit length genome within the viral capsid. The length of the packaged DNA molecule is determined by the size of the viral capsid. Surprisingly, during large DNA cloning experiments, we observed that the
in vitrophage T4 packaging system can package and transduce DNA molecules that are much smaller than the T4 headful size. We analyzed this phenomenon by using defined plasmid DNAs as substrates for
in vitropackaging. The data showed that phage T4 can successfully package and transduce 4 to 29 kb plasmid DNA molecules. When two plasmid DNAs with different antibiotic markers were added to the packaging reaction mixture, transductants that are resistant to both the antibiotics were obtained, suggesting that both the plasmid DNAs are packaged within the same head. Analysis of the transducing particles by equilibrium CsCl density-gradient centrifugation showed that the particles have the same density as the wild-type phage. That the less than headful length molecules were not converted to T4 headful length prior to packaging was established by a number of independent approaches. Finally, unit length plasmid DNA molecules of appropriate size were isolated from the
in vitropackaged particles. Based on these data, we propose a discontinuous headful packaging model for packaging less than headful length molecules. In this model, the packaging machinery packages the first available less than headful length DNA molecule and generates a partially full head. The partially full head then reinitiates packaging on a second DNA molecule. This process continues until the head is filled with DNA.
Inclusive differential cross sections dsigma(pA)/dx(F) and dsigma(pA)/dp(t)(2) for the production of K-S(0), Lambda, and (&ULambda;) over bar particles are measured at HERA in proton-induced ...reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to roots = 41.6 GeV in the proton-nucleon system. The ratios of differential cross sections dsigma(pA)(K-S(0))/dsigma(pA)(Lambda) and dsigma(pA)((&ULambda;) over bar)/dsigma(pA) (Lambda) are measured to be 6.2 +/- 0.5 and 0.66 +/- 0.07, respectively, for x(F) approximate to -0.06. No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions da,Ald t also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections sigma(pA) on the atomic mass A of the target material is discussed, and the deduced cross sections per nucleon sigma(pN) are compared with results obtained at other energies.
Data taken with ten Cosmic Ray Tracking (CRT) detectors and the HEGRA air-shower array on La Palma, Canary Islands, have been analysed to investigate changes of the cosmic
r
ay mass composition at ...the ‘knee’ of the cosmic-ray flux spectrum near 10
15 eV energy. The analysis is based on the angular distributions of particles in air showers. HEGRA data provided the shower size, direction, and core position and CRT data the particle track information. It is shown that the angular distribution of muons in air showers is sensitive to the composition over a wide range of shower sizes and, thus, primary cosmic-ray energies with little systematic uncertainties. Results can be easily expressed in terms of 〈ln
A〉 of primary cosmic rays. In the lower part of the energy range covered, we have considerable overlap with direct composition measurements by the JACEE collaboration and find compatible results in the observed rise of 〈ln
A〉. Above about 10
15 eV energy we find no or at most a slow further rise of 〈ln
A〉. Simple cosmic-ray composition models are presented which are fully consistent with our results as well as the JACEE flux and composition measurements and the flux measurements of the Tibet ASγ collaboration. Minimal three-parameter composition models defined by the same power-law slope of all elements below the knee and a common change in slope at a fixed rigidity are inconsistent with these data.
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