1,203 research outputs found
Ssp1p is a lipid binding protein involved in shaping of the prospore membrane during meiosis in S. cerevisiae
Meiosis is a special form of cell division which results in the formation of haploid cells. At the end of meiosis in yeast four new cells, the so-called spores, are formed inside the boundaries of the mother cell. This morphogenetic process requires de novo formation of the cell membranes. Surprisingly it is the spindle pole bodies (SPBs) which organize the formation of these prospore membranes (PSMs). Membrane vesicles, probably redirected from the secretory pathway, accumulate at the cytoplasmic face of the SPB and fuse to form a continuous membrane system. In our lab we have identified a protein complex which localizes to the tip of this growing membrane, the leading edge protein coat (LEP coat).
In this thesis I demonstrate that the S. cereviaiae protein Ssp1p is a novel component of the LEP coat. It is even the most important constituent of the LEP coat as it recruits all other components to this structure. I can show here that Ssp1p is a lipid binding protein and this affinity is probably required for anchoring the protein complex in the membrane. Ssp1p would then act like a hinge, connecting the PSM to Ady3p, another protein of the LEP coat. Deletion of SSP1 results in a block of sporulation. Here I show that this is most probably due to a defect in membrane shaping. In the deletion mutant the PSM sticks very tightly to the nuclear envelope and closes without incorporating cytoplasm. This later on leads to a defect in spore formation and to a loss of viability. One possible explanation for this phenotype would be that the LEP coat serves as a scaffold which provides some structural stability to the membrane while it grows. The protein ring at its tip might also keep the membrane open until all constituents required are enclosed. In addition to its lipid binding activity it is demonstrated that Ssp1p localizes to the plasma membrane of the bud when it is overexpressed in mitotic cells. This is a hint that Ssp1p might be involved in membrane vesicle targeting. Ssp1p could either be directed to target membranes by their lipid composition or by other interacting proteins. As overexpression of Ssp1p in mitotic cells is toxic some interference with the secretory pathway machinery is proposed.Meiose ist eine spezielle Form der Zellteilung, als Endprodukte entstehen haploide Zellen. In der Bäckerhefe S. cerevisiae werden am Ende der Meiose vier Tochterzellen, die sogenannten Sporen, innerhalb des alten Kompartiments der Mutterzelle gebildet. Dieser Differenzierungsprozess erfordert die komplette Neubildung der äußeren Membranen. Überraschenderweise wird diese Neubildung der sogenannten Prospormembranen von den Spindelpolkörpern organisiert. Membranvesikel, die vermutlich aus dem sekretorischen Pfad stammen, werden umgeleitet und akkumlieren am Spindelpolkörper, wo sie miteinander fusionieren und eine kontinuierliche Membran bilden. In unserem Labor haben wir haben einen Proteinkomplex identifiziert, der an der Spitze dieser wachsenden Membran lokalisiert und dort eine ringförmige Struktur ausbildet.
In dieser Arbeit konnte ich zeigen, daß Ssp1p eine weitere Komponente dieses Proteinkomplexes ist. Ssp1p ist sogar die wichtigste der bisher identifizierten Komponenten, da die Lokalisierung aller anderen Proteine an diese Membranstruktur von Ssp1p abhängt. Die Entdeckung, daß Ssp1p ein Lipid-bindendes Protein ist, erklärt den Aufbau dieser Struktur. Ssp1p interagiert auf der einen Seite mit Ady3p, einem Bestandteil dieses membranständigen Proteinkomplexes, auf der anderen Seite verankert es mittels seiner Fähigkeit zur Lipidbindung den ganzen Komplex in der Membran. Wird SSP1 deletiert so verliert die Zelle die Fähigkeit zur Sporulation. Ich konnte zeigen, daß der Grund hierfür wahrscheinlich in einer Störung der Ausbildung der Prospormembran liegt. In der Deletionsmutante liegt die Prospormembran extrem eng auf der Kernmembran und der Abschluß erfolgt bereits, bevor Cytoplasma eingschlossen werden konnte.
Dies führt dann später zu einem Defekt der Sporenbildung und einem Verlust der Lebensfähigkeit. Eine mögliche Erklärung für die Funktion dieses membranständigen Proteinkomplexes wäre, daß durch sein stabiles Gerüst der wachsenden Membran eine gewisse strukturelle Rigidität gegeben wird. Es ist auch denkbar, daß der Proteinring die Membran geöffnet hält bis alle notwendigen Bestandteile aufgenommen wurden.
Zusätzlich zur Lipidbindungsaktivität von Ssp1p wurde entdeckt, daß Ssp1p, wenn es mitotisch überexprimiert wird, an der Plasmamembran der Tochterzelle (Knospe) lokalisiert. Dies könnte bedeuten, daß Ssp1p eine Rolle bei der Lenkung der sekretorischen Membranvesikel spielt. Durch die Bindung an spezielle Lipide könnte Ssp1p in Membranbereiche gelenkt werden, die Ziele für solche sekretorischen Vesikel darstellen. Diese spezielle Lokalisierung könnte aber auch durch Proteininteraktionen bewirkt werden. Da die Überexpression von Ssp1p für mitotische Zellen toxisch ist liegt es nahe anzunehmen, daß dieses Protein einen Einfluß auf die Funktion der Proteine des sekretorischen Pfades hat
Microwave ISM Emission Observed by WMAP
We investigate the nature of the diffuse Galactic emission in the Wilkinson
Microwave Anisotropy Probe (WMAP) temperature anisotropy data. Substantial
dust-correlated emission is observed at all WMAP frequencies, far exceeding the
expected thermal dust emission in the lowest frequency channels (23, 33, 41
GHz). The WMAP team (Bennett et al.) interpret this emission as dust-correlated
synchrotron radiation, attributing the correlation to the natural association
of relativistic electrons produced by SNae with massive star formation in dusty
clouds, and deriving an upper limit of 5% on the contribution of Draine &
Lazarian spinning dust at K-band (23 GHz). We pursue an alternative
interpretation that much, perhaps most, of the dust-correlated emission at
these frequencies is indeed spinning dust, and explore the spectral dependence
on environment by considering a few specific objects as well as the full sky
average. Models similar to Draine & Lazarian spinning dust provide a good fit
to the full-sky data. The full-sky fit also requires a significant component
with free-free spectrum uncorrelated with \Halpha, possibly hot (~million K)
gas within 30 degrees of the Galactic center.Comment: ApJ in press (accepted 5 Dec 2003), version 2: corrected typos and
added references. 23 pages, 5 figures, 2 tables. Free-free haze map is
available at http://skymaps.inf
Detection of autoantibodies against thyroglobulin, thyroid microsomes, and other soluble antigens with a rational and economical immunoblotting microtechnique
Evidence Of Dark Matter Annihilations In The WMAP Haze
The WMAP experiment has revealed an excess of microwave emission from the
region around the center of our Galaxy. It has been suggested that this signal,
known as the ``WMAP Haze'', could be synchrotron emission from relativistic
electrons and positrons generated in dark matter annihilations. In this letter,
we revisit this possibility. We find that the angular distribution of the WMAP
Haze matches the prediction for dark matter annihilations with a cusped density
profile, in the inner kiloparsecs. Comparing the
intensity in different WMAP frequency bands, we find that a wide range of
possible WIMP annihilation modes are consistent with the spectrum of the haze
for a WIMP with a mass in the 100 GeV to multi-TeV range. Most interestingly,
we find that to generate the observed intensity of the haze, the dark matter
annihilation cross section is required to be approximately equal to the value
needed for a thermal relic, cm/s. No
boost factors are required. If dark matter annihilations are in fact
responsible for the WMAP Haze, and the slope of the halo profile continues into
the inner Galaxy, GLAST is expected to detect gamma rays from the dark matter
annihilations in the Galactic Center if the WIMP mass is less than several
hundred GeV.Comment: 4 pages, 3 figure
Detecting Dark Matter Annihilation with CMB Polarization : Signatures and Experimental Prospects
Dark matter (DM) annihilation during hydrogen recombination (z ~ 1000) will
alter the recombination history of the Universe, and affect the observed CMB
temperature and polarization fluctuations. Unlike other astrophysical probes of
DM, this is free of the significant uncertainties in modelling galactic
physics, and provides a method to detect and constrain the cosmological
abundances of these particles. We parametrize the effect of DM annihilation as
an injection of ionizing energy at a rate e_{dm}, and argue that this simple
"on the spot'' modification is a good approximation to the complicated
interaction of the annihilation products with the photon-electron plasma.
Generic models of DM do not change the redshift of recombination, but change
the residual ionization after recombination. This broadens the surface of last
scattering, suppressing the temperature fluctuations and enhancing the
polarization fluctuations. We use the temperature and polarization angular
power spectra to measure these deviations from the standard recombination
history, and therefore, indirectly probe DM annihilation. (abridged)Comment: 13 pages, 8 figures, submitted to PR
Microwave ISM Emission in the Green Bank Galactic Plane Survey: Evidence for Spinning Dust
We observe significant dust-correlated emission outside of H II regions in
the Green Bank Galactic Plane Survey (-4 < b < 4 degrees) at 8.35 and 14.35
GHz. The rising spectral slope rules out synchrotron and free-free emission as
majority constituents at 14 GHz, and the amplitude is at least 500 times higher
than expected thermal dust emission. When combined with the Rhodes (2.326 GHz),
and WMAP (23-94 GHz) data it is possible to fit dust-correlated emission at
2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an
additional dust-correlated component similar to Draine & Lazarian spinning
dust. The rising component generally dominates free-free and synchrotron for
\nu >~ 14 GHz and is overwhelmed by thermal dust at \nu > 60 GHz. The current
data fulfill most of the criteria laid out by Finkbeiner et al. (2002) for
detection of spinning dust.Comment: ApJ in press. 26 pages, 11 figures, figures jpeg compressed to save
spac
Synthesizing Finite-state Protocols from Scenarios and Requirements
Scenarios, or Message Sequence Charts, offer an intuitive way of describing
the desired behaviors of a distributed protocol. In this paper we propose a new
way of specifying finite-state protocols using scenarios: we show that it is
possible to automatically derive a distributed implementation from a set of
scenarios augmented with a set of safety and liveness requirements, provided
the given scenarios adequately \emph{cover} all the states of the desired
implementation. We first derive incomplete state machines from the given
scenarios, and then synthesis corresponds to completing the transition relation
of individual processes so that the global product meets the specified
requirements. This completion problem, in general, has the same complexity,
PSPACE, as the verification problem, but unlike the verification problem, is
NP-complete for a constant number of processes. We present two algorithms for
solving the completion problem, one based on a heuristic search in the space of
possible completions and one based on OBDD-based symbolic fixpoint computation.
We evaluate the proposed methodology for protocol specification and the
effectiveness of the synthesis algorithms using the classical alternating-bit
protocol.Comment: This is the working draft of a paper currently in submission.
(February 10, 2014
Pseudo-Dipole Signal Removal from WMAP Data
It is discovered in our previous work that different observational
systematics, e.g., errors of antenna pointing directions, asynchronous between
the attitude and science data, can generate pseudo-dipole signal in full-sky
maps of the cosmic microwave background (CMB) anisotropy published by The
Wilkinson Microwave Anisotropy Probe (WMAP) team. Now the antenna sidelobe
response to the Doppler signal is found to be able to produce similar effect as
well. In this work, independent to the sources, we uniformly model the
pseudo-dipole signal and remove it from published WMAP7 CMB maps by model
fitting. The result demonstrates that most of the released WMAP CMB quadrupole
is artificial.Comment: V3: using WMAP7 dat
Constraining the Cosmic Background Light with four BL Lac TeV spectra
The intrinsic BL Lac spectra above few hundreds GeV can be very different
from the observed ones due to the absorption effects by the diffuse
Extragalactic Background Light (EBL), at present poorly known. With the recent
results, there are now 4 sources with good spectral information: Mkn 421
(z=0.031), Mkn 501 (z=0.034), 1ES 1426+428 (z=0.129) and 1ES 1959+650
(z=0.047). Making simple assumptions on the shape of the intrinsic spectra
(according to the present blazar knowledge), we have considered the effects of
different EBL spectral energy distributions (SED) for the first time on all 4
objects together, deriving constraints for the EBL fluxes. These resulted
significantly lower than many direct estimates.Comment: 4 pages, 8 figures; to appear in the proceedings of the 2nd Veritas
Symposium: "TeV Astrophysics of extragalactic sources". April 2003, Chicag
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