317 research outputs found
Identification of sites phosphorylated by the vaccinia virus B1R kinase in viral protein H5R
Background: Vaccinia virus gene B1R encodes a erine/threonine protein kinase. In vitro this protein kinase phosphorylates ribosomal proteins Sa and S2 and vaccinia virus protein H5R, proteins that become phosphorylated during infection. Nothing is known about the sites phosphorylated on these proteins or the general substrate specificity of the kinase. The work described is the first to address these questions.
Results: Vaccinia virus protein H5R was phosphorylated by the B1R protein kinase in vitro, digested with V8 protease, and phosphopeptides separated by HPLC. The N-terminal sequence of one radioactively labelled phosphopeptide was determined and found to correspond to residues 81-87 of the protein, with Thr-84 and Thr-85 being phosphorylated. A synthetic peptide based on this region of the protein was shown to be a substrate for the B1R protein kinase, and the extent of phosphorylation was substantially decreased if either Thr residue was replaced by an Ala.
Conclusions: We have identified the first phosphorylation site for the vaccinia virus B1R protein kinase. This gives important information about the substrate-specificity of the enzyme, which differs from that of other known protein kinases. It remains to be seen whether the same site is phosphorylated in vivo
Coherent phonon dynamics at the martensitic phase transition of Ni_2MnGa
We use time-resolved optical reflectivity to study the laser stimulated
dynamics in the magnetic shape memory alloy Ni_2MnGa. We observe two coherent
optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the
pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a
heavily damped amplitudon respectively. In the martensite phase the martensitic
phase transition can be induced by a fs laser pulse on a timescale of a few ps.Comment: 3 figure
Modeling Sediment Transport in Ice-Walled Subglacial Channels and Its Implications for Esker Formation and Proglacial Sediment Yields
Sediment yields from glacierized basins are used to quantify erosion rates on seasonal to decadal timescales as well as conditions at the glacier bed, and eskers hold valuable information about past subglacial hydraulic conditions in their spatial organization, geometry, and sedimentary structures. Ultimately, eskers are a record of past glacioâfluvial sediment transport, but there is currently no physical model for this process. We develop a 1âD model of morphodynamics in semicircular bedrockâfloored subglacial channels. We adapt a sediment conservation law developed for mixed alluvialâbedrock conditions to subglacial channels. Channel evolution is a function of melt opening by viscous heat dissipation from flowing water and creep closure of the overlying ice, to which we add the closure or enlargement due to sediment deposition or removal, respectively. We apply the model to an idealized landâterminating glacier and find that temporary sediment accumulation in the vicinity of the terminus, or the formation of an incipient esker, is inherent to the dynamics of the channelized water flow. The alluviation of the bed combined with the pressurized channel flow produces unexpected patterns of sediment evacuation: We show that the direction of hysteresis between sediment and water discharge is not necessarily linked to a supplyâ or transportâlimited system, as has been hypothesized for proglacial sediment yields. We also find that the deposition of an incipient esker is a function of a compromise between water discharge and sediment supply, but perhaps more importantly, iceâsurface slope and the temporal pattern of water delivery to the bed
The photoinduced transition in magnetoresistive manganites: a comprehensive view
We use femtosecond x-ray diffraction to study the structural response of
charge and orbitally ordered PrCaMnO thin films across a phase
transition induced by 800 nm laser pulses. By investigating the dynamics of
both superlattice reflections and regular Bragg peaks, we disentangle the
different structural contributions and analyze their relevant time-scales. The
dynamics of the structural and charge order response are qualitatively
different when excited above and below a critical fluence . For
excitations below the charge order and the superlattice is only partially
suppressed and the ground state recovers within a few tens of nanosecond via
diffusive cooling. When exciting above the critical fluence the superlattice
vanishes within approximately half a picosecond followed by a change of the
unit cell parameters on a 10 picoseconds time-scale. At this point all memory
from the symmetry breaking is lost and the recovery time increases by many
order of magnitudes due to the first order character of the structural phase
transition
Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy NiMnGa
Magnetic shape memory Heusler alloys are multiferroics stabilized by the
correlations between electronic, magnetic and structural order. To study these
correlations we use time resolved x-ray diffraction and magneto-optical Kerr
effect experiments to measure the laser induced dynamics in a Heusler alloy
NiMnGa film and reveal a set of timescales intrinsic to the system. We
observe a coherent phonon which we identify as the amplitudon of the modulated
structure and an ultrafast phase transition leading to a quenching of the
incommensurate modulation within 300~fs with a recovery time of a few ps. The
thermally driven martensitic transition to the high temperature cubic phase
proceeds via nucleation within a few ps and domain growth limited by the speed
of sound. The demagnetization time is 320~fs, which is comparable to the
quenching of the structural modulation.Comment: 5 pages, 3 figures. Supplementary materials 5 pages, 5 figure
Statistics of Charge Transport and Modified Time Ordering
The statistics of charge transport across a tunnel junction with energy-dependent scattering is investigated. A model with quadratic dispersion relation is discussed in general and, independently, in the two limiting cases of a large detector and of a linear dispersion relation. The measurement of charge takes place according to various protocols. It is found that, as a rule, the statistics is expressed by means of time-ordered current correlators. However the ordering prescription differs from the usual ones (Dyson and Keldysh) by the Matthews modification. Nevertheless binomial statistics is confirmed in all case
Domain size effects on the dynamics of a charge density wave in 1T-TaS2
Recent experiments have shown that the high temperature incommensurate (I)
charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower
temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved
x-ray diffraction study of the growth process of the photoinduced I-CDW
domains. The layered nature of the material results in a marked anisotropy in
the size of the photoinduced domains of the I-phase. These are found to grow
self-similarly, their shape remaining unchanged throughout the growth process.
The photoinduced dynamics of the newly formed I-CDW phase was probed at various
stages of the growth process using a double pump scheme, where a first pump
creates I-CDW domains and a second pump excites the newly formed I-CDW state.
We observe larger magnitudes of the coherently excited I-CDW amplitude mode in
smaller domains, which suggests that the incommensurate lattice distortion is
less stable for smaller domain sizes.Comment: 8 pages, 8 figure
Structural and magnetic dynamics of a laser induced phase transition in FeRh
We use time-resolved x-ray diffraction and magnetic optical Kerr effect to
study the laser induced antiferromagnetic to ferromagnetic phase transition in
FeRh. The structural response is given by the nucleation of independent
ferromagnetic domains (\tau_1 ~ 30ps). This is significantly faster than the
magnetic response (\tau_2 ~ 60ps) given by the subsequent domain realignment.
X-ray diffraction shows that the two phases co-exist on short time-scales and
that the phase transition is limited by the speed of sound. A nucleation model
describing both the structural and magnetic dynamics is presented.Comment: 5 pages, 3 figures - changed to reflect version accepted for PR
- âŠ