361 research outputs found
USF binding sequences from the HS4 insulator element impose early replication timing on a vertebrate replicator
The nuclear genomes of vertebrates show a highly organized program of DNA replication where GC-rich isochores are replicated early in S-phase, while AT-rich isochores are late replicating. GC-rich regions are gene dense and are enriched for active transcription, suggesting a connection between gene regulation and replication timing. Insulator elements can organize independent domains of gene transcription and are suitable candidates for being key regulators of replication timing. We have tested the impact of inserting a strong replication origin flanked by the β-globin HS4 insulator on the replication timing of naturally late replicating regions in two different avian cell types, DT40 (lymphoid) and 6C2 (erythroid). We find that the HS4 insulator has the capacity to impose a shift to earlier replication. This shift requires the presence of HS4 on both sides of the replication origin and results in an advance of replication timing of the target locus from the second half of S-phase to the first half when a transcribed gene is positioned nearby. Moreover, we find that the USF transcription factor binding site is the key cis-element inside the HS4 insulator that controls replication timing. Taken together, our data identify a combination of cis-elements that might constitute the basic unit of multi-replicon megabase-sized early domains of DNA replication
Phase shift in an atom interferometer induced by the additional laser lines of a Raman laser generated by modulation
The use of Raman laser generated by modulation for light-pulse atom
interferometer allows to have a laser system more compact and robust. However,
the additional laser frequencies generated can perturb the atom interferometer.
In this article, we present a precise calculation of the phase shift induced by
the additional laser frequencies. The model is validated by comparison with
experimental measurements on an atom gravimeter. The uncertainty of the phase
shift determination limits the accuracy of our compact gravimeter at 8.10^-8
m/s^2. We show that it is possible to reduce considerably this inaccuracy with
a better control of experimental parameters or with particular interferometer
configurations
Ramsey interferometry with an atom laser
We present results on a free-space atom interferometer operating on the first
order magnetically insensitive |F=1,mF=0> -> |F=2,mF=0> transition of
Bose-condensed 87Rb atoms. A pulsed atom laser is output-coupled from a
Bose-Einstein condensate and propagates through a sequence of two internal
state beam splitters, realized via coherent Raman transitions between the two
interfering states. We observe Ramsey fringes with a visibility close to 100%
and determine the current and the potentially achievable interferometric phase
sensitivity. This system is well suited to testing recent proposals for
generating and detecting squeezed atomic states.Comment: published version, 8 pages, 3 figure
Theoretical Analysis of a Large Momentum Beamsplitter using Bloch Oscillations
In this paper, we present the implementation of Bloch oscillations in an
atomic interferometer to increase the separation of the two interfering paths.
A numerical model, in very good agreement with the experiment, is developed.
The contrast of the interferometer and its sensitivity to phase fluctuations
and to intensity fluctuations are also calculated. We demonstrate that the
sensitivity to phase fluctuations can be significantly reduced by using a
suitable arrangement of Bloch oscillations pulses
Testing new physics with the electron g-2
We argue that the anomalous magnetic moment of the electron (a_e) can be used
to probe new physics. We show that the present bound on new-physics
contributions to a_e is 8*10^-13, but the sensitivity can be improved by about
an order of magnitude with new measurements of a_e and more refined
determinations of alpha in atomic-physics experiments. Tests on new-physics
effects in a_e can play a crucial role in the interpretation of the observed
discrepancy in the anomalous magnetic moment of the muon (a_mu). In a large
class of models, new contributions to magnetic moments scale with the square of
lepton masses and thus the anomaly in a_mu suggests a new-physics effect in a_e
of (0.7 +- 0.2)*10^-13. We also present examples of new-physics theories in
which this scaling is violated and larger effects in a_e are expected. In such
models the value of a_e is correlated with specific predictions for processes
with violation of lepton number or lepton universality, and with the electric
dipole moment of the electron.Comment: 34 pages, 7 figures. Minor changes and references adde
Charged-Lepton Flavour Physics
This writeup of a talk at the 2011 Lepton-Photon symposium in Mumbai, India,
summarises recent results in the charged-lepton flavour sector. I review
searches for charged-lepton flavour violation, lepton electric dipole moments
and flavour-conserving CP violation. I also discuss recent progress in
tau-lepton physics and in the Standard Model prediction of the muon anomalous
magnetic moment.Comment: Presented at Lepton-Photon 2011, Mumbai, India; 23 pages, 14 figure
Diverse Roles and Interactions of the SWI/SNF Chromatin Remodeling Complex Revealed Using Global Approaches
A systems understanding of nuclear organization and events is critical for determining how cells divide, differentiate, and respond to stimuli and for identifying the causes of diseases. Chromatin remodeling complexes such as SWI/SNF have been implicated in a wide variety of cellular processes including gene expression, nuclear organization, centromere function, and chromosomal stability, and mutations in SWI/SNF components have been linked to several types of cancer. To better understand the biological processes in which chromatin remodeling proteins participate, we globally mapped binding regions for several components of the SWI/SNF complex throughout the human genome using ChIP-Seq. SWI/SNF components were found to lie near regulatory elements integral to transcription (e.g. 5′ ends, RNA Polymerases II and III, and enhancers) as well as regions critical for chromosome organization (e.g. CTCF, lamins, and DNA replication origins). Interestingly we also find that certain configurations of SWI/SNF subunits are associated with transcripts that have higher levels of expression, whereas other configurations of SWI/SNF factors are associated with transcripts that have lower levels of expression. To further elucidate the association of SWI/SNF subunits with each other as well as with other nuclear proteins, we also analyzed SWI/SNF immunoprecipitated complexes by mass spectrometry. Individual SWI/SNF factors are associated with their own family members, as well as with cellular constituents such as nuclear matrix proteins, key transcription factors, and centromere components, implying a ubiquitous role in gene regulation and nuclear function. We find an overrepresentation of both SWI/SNF-associated regions and proteins in cell cycle and chromosome organization. Taken together the results from our ChIP and immunoprecipitation experiments suggest that SWI/SNF facilitates gene regulation and genome function more broadly and through a greater diversity of interactions than previously appreciated
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