2,480 research outputs found
Reduced level of the histone deacetylase Sir2 in mRNA decapping mutants leads to silencing defects and premature aging
No full textRNA metabolism directly or indirectly impacts various cellular pathways.
Mutations in factors involved in mRNA decapping result in phenotypic markers of apoptosis and lead to premature aging. These traits are accompanied by elevated histone mRNA levels persisting throughout the cell cycle and defects in S-phase progression.
Here we show that decapping mutants exhibit low levels of Sir2, which reduces silencing and leads to the elevated transcription of rDNA intergenic spacer regions.
We postulate that defects in decapping are associated with the derepression of silencing at heterochromatic-like regions. This, in turn, may affect histone modification and induce loss of silencing at specific loci, as well as recombination within rDNA repeats, both of which have been shown to regulate cellular lifespan.
References
[1] Mazzoni C, Falcone C. Biochem Soc Trans. (2011), 39(5):1461-5. Review.
[2] Mroczek S & Kufel J (2008).Nucleic Acids Res 36, 2874-2888.
[3]Mazzoni C, Herker E, Palermo V, Jungwirth H, Eisenberg T, Madeo F & Falcone C (2005).EMBO Rep 6, 1076-108.
[4]Palermo V, Cundari E, Mangiapelo E, Falcone C & Mazzoni C (2010).Cell Cycle 9, 3991-3996.
[5] Thompson DM & Parker R (2007).Mol Cell Biol 27, 92-101
Minkowski-Fock states in accelerated frames
No full textAn explicit Wigner formulation of Minkowski particle states for non-inertial observers is unknown. Here, we derive a general prescription to compute the characteristic function for Minkowski-Fock states in accelerated frames. For the special case of single-particle and two-particle states, this method enables to derive mean values of particle numbers and correlation function in the momentum space, and the way they are affected by the acceleration of the observer. We show an indistinguishability between Minkowski single-particle and two-particle states in terms of Rindler particle distribution that can be regarded as a way for the observer to detect any acceleration of the frame. We find that for two-particle states the observer is also able to detect acceleration by measuring the correlation between Rindler particles with different momenta
Observing single-particles beyond the Rindler horizon
No full textWe show that Minkowski single-particle states localized beyond the horizon
modify the Unruh thermal distribution in an accelerated frame. This means that,
contrary to classical predictions, accelerated observers can reveal particles
emitted beyond the horizon. The method we adopt is based on deriving the
explicit Wigner characteristic function for the complete description of the
quantum field in the non-inertial frame and can be generalized to general
states
External and internal triggers of cell death in yeast
No full textIn recent years, yeast was confirmed as a useful eukaryotic model system to decipher the complex mechanisms and networks occurring in higher eukaryotes, particularly in mammalian cells, in physiological as well in pathological conditions. This article focuses attention on the contribution of yeast in the study of a very complex scenario, because of the number and interconnection of pathways, represented by cell death. Yeast, although it is a unicellular organism, possesses the basal machinery of different kinds of cell death occurring in higher eukaryotes, i.e., apoptosis, regulated necrosis and autophagy. Here we report the current knowledge concerning the yeast orthologs of main mammalian cell death regulators and executors, the role of organelles and compartments, and the cellular phenotypes observed in the different forms of cell death in response to external and internal triggers. Thanks to the ease of genetic manipulation of this microorganism, yeast strains expressing human genes that promote or counteract cell death, onset of tumors and neurodegenerative diseases have been constructed. The effects on yeast cells of some of these genes are also presented
Frame-dependence of the non-relativistic limit of quantum fields
No full textWe study the non-relativistic limit of quantum fields for an inertial and a
non-inertial observer. We show that non-relativistic particle states appear as
a superposition of relativistic and non-relativistic particles in different
frames. Hence, the non-relativistic limit is frame-dependent. We detail this
result when the non-inertial observer has uniform constant acceleration. Only
for low accelerations, the accelerated observer agrees with the inertial frame
about the non-relativistic nature of particles locally. In such a
quasi-inertial regime, both observers agree about the number of particles
describing quantum field states. The same does not occur when the acceleration
is arbitrarily large (e.g., the Unruh effect). We furthermore prove that wave
functions of particles in the inertial and the quasi-inertial frame are
identical up to the coordinate transformation relating the two frames
Non-relativistic limit of scalar and Dirac fields in curved spacetime
No full textWe give from first principles the non-relativistic limit of scalar and Dirac
fields in curved spacetime. We aim to find general relativistic corrections to
the quantum theory of particles affected by Newtonian gravity, a regime
nowadays experimentally accessible. We believe that the ever-improving
measurement accuracy and the theoretical interest in finding general
relativistic effects in quantum systems require the introduction of corrections
to the Schr\"{o}dinger-Newtonian theory. We rigorously determine these
corrections by the non-relativistic limit of fully relativistic quantum
theories in curved spacetime. For curved static spacetimes, we show how a
non-inertial observer (equivalently, an observer in the presence of a
gravitational field) can distinguish a scalar field from a Dirac field by
particle-gravity interaction. We study the Rindler spacetime and discuss the
difference between the resulting non-relativistic Hamiltonians. We find that
for sufficiently large acceleration, the gravity-spin coupling dominates over
the corrections for scalar fields, promoting Dirac particles as the best
candidates for observing non-Newtonian gravity in quantum particle
phenomenology
The challenges of multiphase flow metering: Today and beyond
No full textSince the early 1990's, when the first commercial meters started to appear, Multiphase Flow Metering (MFM) has grown from being an area of R&D to representing a discipline in its own right within the oil and gas industry. The total figure for MFM installations worldwide is now over 1,800. Field applications include production optimisation, wet gas metering, mobile well testing and production allocation. However, MFM has not yet achieved its full potential. Despite an impressive improvement in the reliability of sensors and mechanical parts (particularly for subsea installations) over the past few years, there remain unresolved questions regarding the accuracy and range of applicability of today's MFM technology. There is also a tendency to forget the complexity of multiphase flow and to evaluate the overall performance of a MFM as a "black box", often neglecting all the possible uncertainties that are inherent in each individual measurement solutions. This paper reviews the inherent limitations of some classical MFM techniques. It highlights the impact of instruments rangeability, empirical correlations for pressure drop devices and fluids characterisation on the error propagation analysis in the "black box". It also provides a comprehensive review of wet gas definitions for the oil and gas industry. Several attempts have been made to define "wet gas" for the purpose of metering streams at high gas-volume-fractions, but a single definition of wet gas still does not exist. The measurement of multiphase flows presents unique challenges that have not yet been fully resolved. However, the challenges are exciting and the authors have no doubts that new milestones will soon be set in this area. Today's MFM technology has already become one piece of the optimised production system jigsaw. MFM has succeeded in fitting with other technologies toward global field-wide solutions. The ideal MFM of the future is one that provides unambiguous measurements of key parameters from which the flow rates can be deduced independently from flow regimes and fluid properties. Copyright © 2007 by ASME
Minkowski vacuum in Rindler spacetime and Unruh thermal state for Dirac fields
No full textWe consider a free Dirac field in flat spacetime and we derive the
representation of the Minkowski vacuum as an element of the Rindler-Fock space.
We also compute the statistical operator obtained by tracing away the left
wedge. We detail the resulting thermal state for fermionic particles
Isolation and study of KlLSM4, a Kluyveromyces lactis gene homologous to the essential gene LSM4 of Saccharomyces cerevisiae.
No full textWe have isolated the KlLSM4 gene as a multicopy suppressor of a Kluyveromyces lactis mutant which shows a rag(-) phenotype (resistance to antimycin A on glucose). This gene is homologous to the ScLSM4 of Saccharomyces cerevisiae, which codes for an essential 187 amino acid protein containing Sm-like domains. These motifs are present in the evolutionarily conserved family of the Sm-like proteins, which are involved in a large number of cellular processes, including pre-mRNA splicing and mRNA decapping. We demonstrated that the first 72 amino acids of KlLsm4p, which contain the Sm-like domains, can restore cell viability in both K. lactis and S. cerevisiae cells lacking the wild-type protein. However, the absence of the carboxy-terminal region resulted in a remarkable loss of cell viability in the stationary phase. The KlLSM4 sequence has been deposited in the EMBL Data library under Accession No. AJ311719
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