804 research outputs found
Holliday junction resolvase in Schizosaccharomyces pombe has identical endonuclease activity to the CCE1 homologue YDC2
A novel Holliday junction resolving activity has been identified in fractionated cell extracts of the fission yeast Schizosaccharomyces pombe . The enzyme catalyses endonucleolytic cleavage of Holliday junction-containing chi DNA and synthetic four-way DNA junctions. The activity cuts with high specificity a synthetic four-way junction containing a 12 bp core of homologous sequences but has no activity on another four-way junction (with a fixed crossover point), a three-way junction, linear duplex DNA or duplex DNA containing six mismatched nucleotides in the centre. The major cleavage sites map as single nicks in the vicinity of the crossover point, 3' of a thymidine residue. These data indicate that the activity has a strong DNA structure selectivity as well as a limited sequence preference; features similar to the Holliday junction resolving enzymes RuvC of Escherichia coli and the mitochondrial CCE1 (cruciform-cuttingenzyme 1) of Saccharomyces cerevisiae. A putative homologue of CCE1 in S.pombe (YDC2_SCHPO) has been identified through a search of the sequence database. The open reading frame of this gene has been cloned and the encoded protein, YDC2, expressed in E.coli . The purified recombinant YDC2 exhibits Holliday junction resolvase activity and is, therefore, a functional S.pombe homologue of CCE1. The resolvase YDC2 shows the same substrate specificity and produces identical cleavage sites as the activity obtained from S. pombe cells. Both YDC2 and the cellular activity cleave Holliday junctions in both orientations to give nicks that can be ligated in vitro. The partially purified Holliday junction resolving enzyme in fission yeast is biochemically indistinguishable from recombinant YDC2 and appears to be the same protein
Sequential noise-induced escapes for oscillatory network dynamics
It is well known that the addition of noise in a multistable system can
induce random transitions between stable states. The rate of transition can be
characterised in terms of the noise-free system's dynamics and the added noise:
for potential systems in the presence of asymptotically low noise the
well-known Kramers' escape time gives an expression for the mean escape time.
This paper examines some general properties and examples of transitions between
local steady and oscillatory attractors within networks: the transition rates
at each node may be affected by the dynamics at other nodes. We use first
passage time theory to explain some properties of scalings noted in the
literature for an idealised model of initiation of epileptic seizures in small
systems of coupled bistable systems with both steady and oscillatory
attractors. We focus on the case of sequential escapes where a steady attractor
is only marginally stable but all nodes start in this state. As the nodes
escape to the oscillatory regime, we assume that the transitions back are very
infrequent in comparison. We quantify and characterise the resulting sequences
of noise-induced escapes. For weak enough coupling we show that a master
equation approach gives a good quantitative understanding of sequential
escapes, but for strong coupling this description breaks down
Fast and slow domino regimes in transient network dynamics
It is well known that the addition of noise to a multistable dynamical system
can induce random transitions from one stable state to another. For low noise,
the times between transitions have an exponential tail and Kramers' formula
gives an expression for the mean escape time in the asymptotic limit. If a
number of multistable systems are coupled into a network structure, a
transition at one site may change the transition properties at other sites. We
study the case of escape from a "quiescent" attractor to an "active" attractor
in which transitions back can be ignored. There are qualitatively different
regimes of transition, depending on coupling strength. For small coupling
strengths the transition rates are simply modified but the transitions remain
stochastic. For large coupling strengths transitions happen approximately in
synchrony - we call this a "fast domino" regime. There is also an intermediate
coupling regime some transitions happen inexorably but with a delay that may be
arbitrarily long - we call this a "slow domino" regime. We characterise these
regimes in the low noise limit in terms of bifurcations of the potential
landscape of a coupled system. We demonstrate the effect of the coupling on the
distribution of timings and (in general) the sequences of escapes of the
system.Comment: 3 figure
Sequential escapes: onset of slow domino regime via a saddle connection
We explore sequential escape behaviour of coupled bistable systems under the
influence of stochastic perturbations. We consider transient escapes from a
marginally stable "quiescent" equilibrium to a more stable "active"
equilibrium. The presence of coupling introduces dependence between the escape
processes: for diffusive coupling there is a strongly coupled limit (fast
domino regime) where the escapes are strongly synchronised while for
intermediate coupling (slow domino regime) without partially escaped stable
states, there is still a delayed effect. These regimes can be associated with
bifurcations of equilibria in the low-noise limit. In this paper we consider a
localized form of non-diffusive (i.e pulse-like) coupling and find similar
changes in the distribution of escape times with coupling strength. However we
find transition to a slow domino regime that is not associated with any
bifurcations of equilibria. We show that this transition can be understood as a
codimension-one saddle connection bifurcation for the low-noise limit. At
transition, the most likely escape path from one attractor hits the escape
saddle from the basin of another partially escaped attractor. After this
bifurcation we find increasing coefficient of variation of the subsequent
escape times
A PRACTICAL APPROACH FOR INTEGRATING HETEROGENEOUS SYSTEMS
The adoption of cloud computing is a major requirement for expanding a conventional business into an electronic one. In order to benefit fully from the advantages of cloud computing, companies need to have their business applications redesigned, yet this requires substantial financial, human and time resources which even the largest enterprises cannot afford. A feasible option is developing a strategy for gradual transition to cloud systems and technologies, which implies integrating the conventional systems of enterprises with newly developed cloud solutions.
The underlying idea of this research is that the priorities of such gradual transition should be identified on the basis of the major characteristics of the activities comprising the overall business process, such as its dynamics and prospects, the current and the potential level of automation, the volume of processed data, the workload they create for the systems processing those data, etc.
The research paper proposes an approach for integrating a conventional and a cloud system to service the business process ‘Requesting a consumer loan’ that requires real-time data exchange. The integration solution uses data structures which have been created in an intermediate data base for communication between systems. The rules for accessing and manipulating data by each of the integrated systems are defined. Interoperability is ensured through programme components (triggers and stored procedures) that are created in the data base of the operational system and ensure data exchange for real-time processing. The approach proposed in the paper has been employed in the business practice of a large Bulgarian bank. Its major advantages relate to the comprehensive service of the business process, as well as the greater flexibility, adaptability and scalability achieved with minimum financial and time resources
Reflections on Church-Based English Ministry
This article provides a reflection on lessons learned in directing a church-based ESL program in the United States. The author reflects on stories of God’s provision, the importance of preparing and teaching well, the deeply relational aspects of this ministry, the integration of the Body of Christ, and the importance of encouraging and supporting volunteers in these programs. Special consideration is given to the scope and purpose of church-based English programs and the ways that TESOL professionals can support volunteer teachers in this work
Modeling Joint Improvisation between Human and Virtual Players in the Mirror Game
Joint improvisation is observed to emerge spontaneously among humans
performing joint action tasks, and has been associated with high levels of
movement synchrony and enhanced sense of social bonding. Exploring the
underlying cognitive and neural mechanisms behind the emergence of joint
improvisation is an open research challenge. This paper investigates the
emergence of jointly improvised movements between two participants in the
mirror game, a paradigmatic joint task example. A theoretical model based on
observations and analysis of experimental data is proposed to capture the main
features of their interaction. A set of experiments is carried out to test and
validate the model ability to reproduce the experimental observations. Then,
the model is used to drive a computer avatar able to improvise joint motion
with a human participant in real time. Finally, a convergence analysis of the
proposed model is carried out to confirm its ability to reproduce the emergence
of joint movement between the participants
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