562 research outputs found
Pay32p of the Yeast Yarrowia lipolytica Is an Intraperoxisomal Component of the Matrix Protein Translocation Machinery
Pay mutants of the yeast Yarrowia lipolytica fail to assemble functional peroxisomes. One mutant strain, pay32-1, has abnormally small peroxisomes that are often found in clusters surrounded by membranous material. The functionally complementing gene PAY32 encodes a protein, Pay32p, of 598 amino acids (66,733 D) that is a member of the tetratricopeptide repeat family. Pay32p is intraperoxisomal. In wild-type peroxisomes, Pay32p is associated primarily with the inner surface of the peroxisomal membrane, but ~30% of Pay32p is localized to the peroxisomal matrix. The majority of Pay32p in the matrix is complexed with two polypeptides of 62 and 64 kD recognized by antibodies to SKL (peroxisomal targeting signal-1). In contrast, in peroxisomes of the pay32-1 mutant, Pay32p is localized exclusively to the matrix and forms no complex. Biochemical characterization of the mutants pay32-1 and pay32-KO (a PAY32 gene disruption strain) showed that Pay32p is a component of the peroxisomal translocation machinery. Mutations in the PAY32 gene prevent the translocation of most peroxisome-bound proteins into the peroxisomal matrix. These proteins, including the 62-kD anti-SKL-reactive polypeptide, are trapped in the peroxisomal membrane at an intermediate stage of translocation in pay32 mutants. Our results suggest that there are at least two distinct translocation machineries involved in the import of proteins into peroxisomes.
Toward physical realizations of thermodynamic resource theories
Conventional statistical mechanics describes large systems and averages over
many particles or over many trials. But work, heat, and entropy impact the
small scales that experimentalists can increasingly control, e.g., in
single-molecule experiments. The statistical mechanics of small scales has been
quantified with two toolkits developed in quantum information theory: resource
theories and one-shot information theory. The field has boomed recently, but
the theorems amassed have hardly impacted experiments. Can thermodynamic
resource theories be realized experimentally? Via what steps can we shift the
theory toward physical realizations? Should we care? I present eleven
opportunities in physically realizing thermodynamic resource theories.Comment: Publication information added. Cosmetic change
Breakdown of the Landauer bound for information erasure in the quantum regime
A known aspect of the Clausius inequality is that an equilibrium system
subjected to a squeezing \d S of its entropy must release at least an amount
|\dbarrm Q|=T|\d S| of heat. This serves as a basis for the Landauer
principle, which puts a lower bound for the heat generated by erasure
of one bit of information. Here we show that in the world of quantum
entanglement this law is broken. A quantum Brownian particle interacting with
its thermal bath can either generate less heat or even {\it adsorb} heat during
an analogous squeezing process, due to entanglement with the bath. The effect
exists even for weak but fixed coupling with the bath, provided that
temperature is low enough. This invalidates the Landauer bound in the quantum
regime, and suggests that quantum carriers of information can be much more
efficient than assumed so far.Comment: 13 pages, revtex, 2 eps figure
Spectroscopic follow-up of TESS candidates with KESPRINT 1.5 - 3-m telescopes network
We report on the spectroscopic follow-up of TESS planetary candidates with a network of 2-3 meter telescopes located in Ondrejov, CZ, Tautenburg, DE, McDonald observatory, US and SMARTS telescope, CL, which use spectrographs with high resolving power. We coordinate our observing campaigns within the KESPRINT consortium and we significantly contribute to validation and characterization of mostly gas giant planets but not only. We briefly present involved observatories and their current observing campaigns
Performance of discrete heat engines and heat pumps in finite time
The performance in finite time of a discrete heat engine with internal
friction is analyzed. The working fluid of the engine is composed of an
ensemble of noninteracting two level systems. External work is applied by
changing the external field and thus the internal energy levels. The friction
induces a minimal cycle time. The power output of the engine is optimized with
respect to time allocation between the contact time with the hot and cold baths
as well as the adiabats. The engine's performance is also optimized with
respect to the external fields. By reversing the cycle of operation a heat pump
is constructed. The performance of the engine as a heat pump is also optimized.
By varying the time allocation between the adiabats and the contact time with
the reservoir a universal behavior can be identified. The optimal performance
of the engine when the cold bath is approaching absolute zero is studied. It is
found that the optimal cooling rate converges linearly to zero when the
temperature approaches absolute zero.Comment: 45 pages LaTeX, 25 eps figure
Quantum Theory and Time Asymmetry
The relation between quantum measurement and thermodynamically irreversible
processes is investigated. The reduction of the state vector is fundamentally
asymmetric in time and shows an observer-relatedness which may explain the
double interpretation of the state vector as a representation of physical
states as well as of information about them. The concept of relevance being
used in all statistical theories of irreversible thermodynamics is shown to be
based on the same observer-relatedness. Quantum theories of irreversible
processes implicitly use an objectivized process of state vector reduction. The
conditions for the reduction are discussed, and I speculate that the final
(subjective) observer system might even be carried by a spacetime point.Comment: Latex version of a paper published in 1979 (with minor revisions), 18
page
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress
Cytogerontology, the science of cellular ageing, originated in 1881 with the prediction by August Weismann that the somatic cells of higher animals have limited division potential. Weismann's prediction was derived by considering the role of natural selection in regulating the duration of an organism's life. For various reasons, Weismann's ideas on ageing fell into neglect following his death in 1914, and cytogerontology has only reappeared as a major research area following the demonstration by Hayflick and Moorhead in the early 1960s that diploid human fibroblasts are restricted to a finite number of divisions in vitro.
In this review we give a detailed account of Weismann's theory, and we reveal that his ideas were both more extensive in their scope and more pertinent to current research than is generally recognised. We also appraise the progress which has been made over the past hundred years in investigating the causes of ageing, with particular emphasis being given to (i) the evolution of ageing, and (ii) ageing at the cellular level. We critically assess the current state of knowledge in these areas and recommend a series of points as primary targets for future research
Fusion of Small Peroxisomal Vesicles in Vitro Reconstructs an Early Step in the in Vivo Multistep Peroxisome Assembly Pathway of Yarrowia lipolytica
We have identified and purified six subforms of peroxisomes, designated P1 to P6, from the yeast, Yarrowia lipolytica. An analysis of trafficking of peroxisomal proteins in vivo suggests the existence of a multistep peroxisome assembly pathway in Y. lipolytica. This pathway operates by conversion of peroxisomal subforms in the direction P1, P2→P3→P4→P5→P6 and involves the import of various peroxisomal proteins into distinct vesicular intermediates. We have also reconstituted in vitro the fusion of the earliest intermediates in the pathway, small peroxisomal vesicles P1 and P2. Their fusion leads to the formation of a larger and more dense peroxisomal vesicle, P3. Fusion of P1 and P2 in vitro requires cytosol and ATP hydrolysis and is inhibited by antibodies to two membrane-associated ATPases of the AAA family, Pex1p and Pex6p. We provide evidence that the fusion in vitro of P1 and P2 peroxisomes reconstructs an actual early step in the peroxisome assembly pathway operating in vivo in Y. lipolytica
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