1,637 research outputs found
Insights into the activation mechanism of PopA, a cyclic di-GMP effector protein involved in cell cycle and development of "Caulobacter Crescentus"
No full textIn Caulobacter crescentus, a complex network integrating cyclic di-GMP and Phosphorylation-dependent signals controls the proteolysis of key regulatory proteins to drive cell cycle and polar morphogenesis. The c-di-GMP input is processed by the effector protein PopA. Upon binding of c-di-GMP, PopA is sequestered to the old cell pole where it recruits the replication and cell division inhibitors CtrA and KidO and mediates their destruction by the polar ClpXP protease prior to entry into S-phase. In addition to its role at the stalked cell pole, PopA localizes to the opposite cell pole in dependence of the general topology factor PodJ where it exerts a yet unknown function.
Here we address the activation and polar sequestration mechanism of PopA guided by an existing activation model for the highly homologous c-di-GMP signaling protein PleD. PopA and PleD do not only share an identical domain organization (Rec1-Rec2-GGDEF), but also show similar spatio-temporal behavior during the cell cycle. While PleD is activated and targeted to the old cell pole via phosphorylation-induced dimerization, we show that PopA stalked pole function is phosphorylation-independent and requires c-di-GMP binding as a primary input signal for activation and polar localization. c-di-GMP binds to conserved primary and secondary I-sites within the PopA GGDEF domain and we show that intact binding sites are required for PopA positioning and function. This suggests that c-di-GMP-dependent crosslinking of adjacent GGDEF domains contributes to the localization of an active PopA dimer to the cell pole. Consistent with this, we demonstrate that the GGDEF domain encodes the polar localization signal(s), while the N-terminal receiver domains serve as interaction platform for downstream components that are actively recruited by PopA.
Among these downstream factors is RcdA, a small mediator protein that interacts with the first PopA receiver domain and helps to recruit and degrade CtrA and KidO. In a screen for additional components of the PopA pathway we identify two novel proteins that directly interact with PopA, CC1462 and CC2616. CC1462 is a ClpXP substrate that requires PopA for polar positioning and subsequent degradation during swarmer-to-stalked cell transition. Although located in a flagellar gene cluster, deletion of CC1462 did not affect flagellar assembly and function. Its cellular role as well as the significance of its cell cycle-dependent degradation requires further studies. CC2616, the second PopA interaction partner, is not proteolytically processed and thus belongs to another class of PopA-dependent substrates. CC2616 is annotated as guanine deaminase, which is predicted to catalyze the conversion from guanine to xanthine thereby irreversibly removing guanine based nucleotides from a cellular pool. A CC2616 deletion leads to increased attachment and decreased motility, a phenocopy of strains with elevated c-di-GMP levels. It is not clear whether CC2616 indeed has deaminase activity or whether it has adopted a novel function.
Taken together, this work provides insight into the activation mechanism of a c-di-GMP effector protein. We propose that PopA has evolved through gene duplication from its ancestor, the catalytic PleD response regulator but has lost catalytic activity of the diguanylate cyclase domain. Moreover, PopA has adopted an inverse intra-molecular information transfer originating through c-di-GMP binding at the C-terminal GGDEF domain, which in turn activates the N-terminal receiver stem to serve as platform for downstream partner recruitment
Liquid structure of Rb-Hg alloys studied by neutron diffraction
No full textThe structures of liquid Rb–Hg alloys were studied as a function of composition by neutron diffraction. In the intermediate Rb concentration range, the obtained structure factors show a small prepeak, which may be an evidence of the formation of Hg polyanion units in liquids. The Reverse Monte Carlo (RMC) analysis was applied to separate the total radial distribution function into the corresponding partial radial distribution functions. Up to 10 at.% Rb, no obvious changes are found for the first peak position of the partial radial distribution functions of the Hg–Hg pair and that of the Hg–Rb pair. The first peak position between the Hg–Rb pairs increases above 20 at.% Rb. In addition to the first peak, a subpeak between Hg–Hg pairs can be seen in the large distance. At 60 at.% Rb, the nearest neighbor distance between Hg atoms shows the closest value in the concentration range studied. These results indicate that with the progress of charge transfer the solvation structure in the dilute Rb concentration range changes into the structure containing polyanions composed of Hg species
Fractional Edge Cover Number of Model RB
No full textModel RB is a random constraint satisfaction problem with a growing domain size, which exhibits exact phase transition phenomena. Many hard instances with planted solutions can be generated via Model RB, to be used as benchmarks for algorithmic competitions and researches. In the past, some structural parameters of constraint hypergraphs are analyzed to show hardness of Model RB, such as hinge width, decycling number, treewidth, and hypertree width. In this paper, one more structural parameter of constraint hypergraphs of Model RB, namely the fractional edge cover number, is analyzed. We show upper and lower bounds on the fractional edge cover number of Model RB. In particular, the fractional edge cover number of Model RB is shown to be asymptotically linear in the number of variables, like hinge width, decycling number, treewidth and hypertree width. These results together provide further evidences on the hardness of Model RB.EICPCI-S(ISTP)[email protected]
MILLIMETER-WAVE SPECTROSCOPY OF COLD RB ATOMS
No full textAuthor Institution: Department of Physics, University of Virginia, McCormick Road, Charlottesville, Virginia 22903Cold Rb atoms were prepared by magneto-optical trap. Millimeter-wave has been used to drive nd to (n-2)f one-photon and nd to (n-1)g () two-photon transitions. Quantum defects of f and g states of Rb were calculated. Full analyses will be presented. }
Interpretation and the Problem of the Intention of the Author, by Burhanetir Tatar
No full textBurhanetir Tatar, Interpretation and the Problem of the Intention of the Author: H.G. Gadamer vs E.D. Hirsh, The Council for Research in Values and Philosophy, 199
Aneuploidy in spermatids of Robertsonian (Rb) chromosome heterozygous mice
No full text© 2014, The Author(s). Rb translocations are chromosomal rearrangements frequently found in natural populations of the house mouse Mus musculus domesticus. The standard diploid karyotype of the house mouse consisting of 40 telocentric chromosomes may be reduced by the emergence of metacentric Rb chromosomes. Multiple simple Rb heterozygotes form trivalents exhibiting higher anaphase nondisjunction frequency and consequently higher number of unbalanced gametes than in normal males. This work will attempt to establish whether frequencies of aneuploidy observed in heterozygote spermatids of the house mouse M. musculus domesticus show differences in chromosomes derived from different trivalents. Towards this goal, the number and distribution frequency of aneuploidy was assessed via FISH staining of specific chromosomes of spermatids derived from 2n = 32 individuals. Our results showed that for a given set of target chromosomes, 90 % of the gametes were balanced, resulting from alternate s
Synthesis and Characterization of Multiple-Cation Rb(MAFA)PbI3 Perovskite Single Crystals
No full textWe synthesized multiple-cation Rb(MAFA)PbI3 perovskite single crystals for the first time. The effect of Rb+ substitution was systemically investigated, and the addition of 1.5 M 5% RbI was the optimum condition to obtain high-quality Rb(MAFA)PbI3 single crystals. Lattice shrinkage occurred in the Rb(MAFA)PbI3 single crystal because of the small ionic radius of Rb+, resulting in blue-shifted absorption and photoluminescence (PL) peaks. The 1.5 M 5% RbI-added (MAFA)PbI3 single crystal showed the longest carrier lifetime of 18.35 ns, exhibiting the highest photoresponse than other crystals. We believe that this work will provide a basic insight into the mixed-cation perovskite single crystals for the future optoelectronic applications. © The Author(s) 201
TEMPERATURE DEPENDENCE OF AND (n=3-5) CLUSTER IONS
No full textAuthor Institution: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801Competition between ionwater electrostatic interactions and waterwater hydrogen bonding allows several structural isomers of hydrated rubidium cluster ions to exist simultaneously. The cluster ion temperature plays a large role in determining which of these non-covalent interactions will dominate. Colder temperatures favor isomers with multiple hydrogen bonds while warmer temperatures favor less-structured isomers with fewer hydrogen bonds. The temperature, or internal energy, of hydrated rubidium cluster ions is controlled by varying the evaporative path available for cluster formation. If the evaporation involves loss of water molecules, the final cluster ion temperature will be in the range of . Evaporation of argon atoms generates substantially colder cluster ions with temperatures of . Infrared photodissociation spectra of are compared with \textit{(n=3-5)} spectra to illustrate entropic effects on the relative abundance of structural isomers in clusters. The identification of isomers present is aided by parallel \textit{ab initio}, RRKM-EE and thermodynamics calculations
Lagrangian analysis of turbulent rotating convection
No full textThis study aims to explore how the flow transition from one state to the other in rotating convection will affect the Lagrangian statistics of (fluid) particles. 3D Particle Tracking Velocimetry (3D-PTV) is employed in a water-filled cylindrical tank of equal height and diameter 200 mm. The measurements are performed in the central volume of 50 × 50 × 50 mm3 at a Rayleigh number Ra = 1.28 × 109 and Prandtl number Pr = 6.7. We are reporting the velocity and acceleration pdfs for different Rossby numbers. For different rotation rates, the transverse velocity pdfs show a Gaussian distribution. The vertical velocity pdf has slightly wider tails for stationary and high rotation rate cases, while it approaches the Gaussian distribution for intermediate rotation rates. The acceleration pdfs have significantly wider tails in comparison to those of a Gaussian distribution which is similar to the other turbulent flows. Increasing rotation results in less intermittency in vertical acceleration in the center of RB
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