2,701 research outputs found
Cdc6 ATPase activity disengages Cdc6 from the pre-replicative complex to promote DNA replication
© 2015, Chang et al.To initiate DNA replication, cells first load an MCM helicase double hexamer at origins in a reaction requiring ORC, Cdc6, and Cdt1, also called pre-replicative complex (pre-RC) assembly. The essential mechanistic role of Cdc6 ATP hydrolysis in this reaction is still incompletely understood. Here, we show that although Cdc6 ATP hydrolysis is essential to initiate DNA replication, it is not essential for MCM loading. Using purified proteins, an ATPase-defective Cdc6 mutant ‘Cdc6-E224Q’ promoted MCM loading on DNA. Cdc6-E224Q also promoted MCM binding at origins in vivo but cells remained blocked in G1-phase. If after loading MCM, Cdc6-E224Q was degraded, cells entered an apparently normal S-phase and replicated DNA, a phenotype seen with two additional Cdc6 ATPase-defective mutants. Cdc6 ATP hydrolysis is therefore required for Cdc6 disengagement from the pre-RC after helicase loading to advance subsequent steps in helicase activation in vivo
Devitrification of the Kob-Andersen glass former: Competition with the locally favored structure
Supercooled liquids are kinetically trapped materials in which the transition
to a thermodynamically more stable state with long-range order is strongly
suppressed. To assess the glass-forming abilities of a liquid empirical rules
exist, but a comprehensive microscopic picture of devitrification is still
missing. Here we study the crystallization of a popular model glass former, the
binary Kob-Andersen mixture, in small systems. We perform trajectory sampling
employing the population of the locally favored structure as order parameter.
While for large population a dynamical phase transition has been reported, here
we show that biasing towards a small population of locally favored structures
induces crystallization, and we estimate the free energy difference. This
result sheds new light on the competition between local and global structure in
glass-forming liquids and its implications for crystallization
Non-Equilibrium Phase Transition in an Atomistic Glassformer: the Connection to Thermodynamics
Tackling the low-temperature fate of supercooled liquids is challenging due
to the immense timescales involved, which prevent equilibration and lead to the
operational glass transition. Relating glassy behaviour to an underlying,
thermodynamic phase transition is a long-standing open question in condensed
matter physics. Like experiments, computer simulations are limited by the small
time window over which a liquid can be equilibrated. Here we address the
challenge of low temperature equilibration using trajectory sampling in a
system undergoing a nonequilibrium phase transition. This transition occurs in
trajectory space between the normal supercooled liquid and a glassy state rich
in low-energy geometric motifs. Our results indicate that this transition might
become accessible in equilibrium configurational space at a temperature close
to the so-called Kauzmann temperature, and provide a possible route to unify
dynamical and thermodynamical theories of the glass transition.Comment: accepted in Physical. Rev.
Traveling-wave tube reliability estimates, life tests, and space flight experience
Infant mortality, useful life, and wearout phase of twt life are considered. The performance of existing developmental tubes, flight experience, and sequential hardware testing are evaluated. The reliability history of twt's in space applications is documented by considering: (1) the generic parts of the tube in light of the manner in which their design and operation affect the ultimate reliability of the device, (2) the flight experience of medium power tubes, and (3) the available life test data for existing space-qualified twt's in addition to those of high power devices
Spontaneous Radiofrequency Emission from Hot-Electron Plasmas
Contains report on one research project.United States Atomic Energy Commission under Contract AT(30-1)-358
Characterizing Potentials by a Generalized Boltzmann Factor
Based on the concept of a nonequilibrium steady state, we present a novel
method to experimentally determine energy landscapes acting on colloidal
systems. By measuring the stationary probability distribution and the current
in the system, we explore potential landscapes with barriers up to several
hundred \kT. As an illustration, we use this approach to measure the
effective diffusion coefficient of a colloidal particle moving in a tilted
potential
Cdc6 ATPase activity regulates ORC center dot Cdc6 stability and the selection of specific DNA sequences as origins of DNA replication
DNA replication, as with all macromolecular synthesis steps, is controlled in part at the level of initiation. Although the origin recognition complex ( ORC) binds to origins of DNA replication, it does not solely determine their location. To initiate DNA replication ORC requires Cdc6 to target initiation to specific DNA sequences in chromosomes and with Cdt1 loads the ring-shaped mini-chromosome maintenance ( MCM) 2-7 DNA helicase component onto DNA. ORC and Cdc6 combine to form a ring-shaped complex that contains six AAA(+) subunits. ORC and Cdc6 ATPase mutants are defective in MCM loading, and ORC ATPase mutants have reduced activity in ORC.Cdc6.DNA complex formation. Here we analyzed the role of the Cdc6 ATPase on ORC.Cdc6 complex stability in the presence or absence of specific DNA sequences. Cdc6 ATPase is activated by ORC, regulates ORC.Cdc6 complex stability, and is suppressed by origin DNA. Mutations in the conserved origin A element, and to a lesser extent mutations in the B1 and B2 elements, induce Cdc6 ATPase activity and prevent stable ORC.Cdc6 formation. By analyzing ORC.Cdc6 complex stability on various DNAs, we demonstrated that specific DNA sequences control the rate of Cdc6 ATPase, which in turn controls the rate of Cdc6 dissociation from the ORC.Cdc6.DNA complex. We propose a mechanism explaining how Cdc6 ATPase activity promotes origin DNA sequence specificity; on DNA that lacks origin activity, Cdc6 ATPase promotes dissociation of Cdc6, whereas origin DNA down-regulates Cdc6 ATPase resulting in a stable ORC.Cdc6.DNA complex, which can then promote MCM loading. This model has relevance for origin specificity in higher eukaryotes
On the hyperbolicity and causality of the relativistic Euler system under the kinetic equation of state
We show that a pair of conjectures raised in [11] concerning the construction
of normal solutions to the relativistic Boltzmann equation are valid. This
ensures that the results in [11] hold for any range of positive temperatures
and that the relativistic Euler system under the kinetic equation of state is
hyperbolic and the speed of sound cannot overcome .Comment: 6 pages. Abridged version; full version to appear in Commun. Pure
Appl. Ana
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