986 research outputs found
Hyperphosphorylation amplifies UPF1 activity to resolve stalls in nonsense-mediated mRNA decay.
Many gene expression factors contain repetitive phosphorylation sites for single kinases, but the functional significance is poorly understood. Here we present evidence for hyperphosphorylation as a mechanism allowing UPF1, the central factor in nonsense-mediated decay (NMD), to increasingly attract downstream machinery with time of residence on target mRNAs. Indeed, slowing NMD by inhibiting late-acting factors triggers UPF1 hyperphosphorylation, which in turn enhances affinity for factors linking UPF1 to decay machinery. Mutational analyses reveal multiple phosphorylation sites contributing to different extents to UPF1 activity with no single site being essential. Moreover, the ability of UPF1 to undergo hyperphosphorylation becomes increasingly important for NMD when downstream factors are depleted. This hyperphosphorylation-dependent feedback mechanism may serve as a molecular clock ensuring timely degradation of target mRNAs while preventing degradation of non-targets, which, given the prevalence of repetitive phosphorylation among central gene regulatory factors, may represent an important general principle in gene expression
Single-Quadrature Continuous-Variable Quantum Key Distribution
Most continuous-variable quantum key distribution schemes are based on the
Gaussian modulation of coherent states followed by continuous quadrature
detection using homodyne detectors. In all previous schemes, the Gaussian
modulation has been carried out in conjugate quadratures thus requiring two
independent modulators for their implementations. Here, we propose and
experimentally test a largely simplified scheme in which the Gaussian
modulation is performed in a single quadrature. The scheme is shown to be
asymptotically secure against collective attacks, and considers asymmetric
preparation and excess noise. A single-quadrature modulation approach renders
the need for a costly amplitude modulator unnecessary, and thus facilitates
commercialization of continuous-variable quantum key distribution.Comment: 13 pages, 7 figure
Continuous Variable Quantum Key Distribution with a Noisy Laser
Existing experimental implementations of continuous-variable quantum key
distribution require shot-noise limited operation, achieved with shot-noise
limited lasers. However, loosening this requirement on the laser source would
allow for cheaper, potentially integrated systems. Here, we implement a
theoretically proposed prepare-and-measure continuous-variable protocol and
experimentally demonstrate the robustness of it against preparation noise
stemming for instance from technical laser noise. Provided that direct
reconciliation techniques are used in the post-processing we show that for
small distances large amounts of preparation noise can be tolerated in contrast
to reverse reconciliation where the key rate quickly drops to zero. Our
experiment thereby demonstrates that quantum key distribution with
non-shot-noise limited laser diodes might be feasible.Comment: 10 pages, 6 figures. Corrected plots for reverse reconciliatio
Audiovisual Integration of Speech in a Patient with Broca’s Aphasia
Lesions to Broca’s area cause aphasia characterised by a severe impairment of the ability to speak, with comparatively intact speech perception. However, some studies have found effects on speech perception under adverse listening conditions, indicating that Broca’s area is also involved in speech perception. While these studies have focused on auditory speech perception other studies have shown that Broca’s area is activated by visual speech perception. Furthermore, one preliminary report found that a patient with Broca’s aphasia did not experience the McGurk illusion suggesting that an intact Broca’s area is necessary for audiovisual integration of speech. Here we describe a patient with Broca’s aphasia who experienced the McGurk illusion. This indicates that an intact Broca’s area is not necessary for audiovisual integration of speech. The McGurk illusions this patient experienced were atypical, which could be due to Broca’s area having a more subtle role in audiovisual integration of speech. The McGurk illusions of a control subject with Wernicke’s aphasia were, however, also atypical. This indicates that the atypical McGurk illusions were due to deficits in speech processing that are not specific to Broca’s aphasia
The Attentional Blink is Modulated by First Target Contrast: Implications of an Attention Capture Hypothesis
When two targets (T1 & T2) are presented in rapid succession, observers often fail to report T2 if they attend to T1. The bottleneck theory proposes that this attentional blink (AB) is due to T1 occupying a slow processing stage when T2 is presented. Accordingly, if increasing T1 difficulty increases T1 processing time, this should cause a greater AB. The attention capture hypothesis suggests that T1 captures attention, which cannot be reallocated to T2 in time. Accordingly, if increasing T1 difficulty decreases T1 saliency, this should cause a smaller AB. In two experiments we find support for an attention capture hypothesis. In Experiment 1 we find that AB magnitude increases with T1 contrast – but only when T1 is unmasked. In Experiment 2 we add Gaussian noise to targets and vary T1 contrast but keep T1‘s SNR constant. Again we find that AB magnitude increases with T1 contrast
Super sensitivity and super resolution with quantum teleportation
We propose a method for quantum enhanced phase estimation based on continuous
variable (CV) quantum teleportation. The phase shift probed by a coherent state
can be enhanced by repeatedly teleporting the state back to interact with the
phase shift again using a supply of two-mode squeezed vacuum states. In this
way, both super resolution and super sensitivity can be obtained due to the
coherent addition of the phase shift. The protocol enables Heisenberg limited
sensitivity and super- resolution given sufficiently strong squeezing. The
proposed method could be implemented with current or near-term technology of CV
teleportation.Comment: 5 pagers, 3 figure
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