569 research outputs found
dUTPase based switch controls transfer of virulence genes in order to preserve integrity of the transferred mobile genetic elements
dUTPases ubiquitously regulate cellular dUTP levels to preserve
genome integrity. Recently, several other cellular processes were
reported to be controlled by dUTPases including the horizontal
transfer of Staphylococcus aureus pathogenicity islands (SaPI).
SaPIs are mobil genetic elements that encode virulence enhancing
factors e.g. toxins. Here, phage dUTPases were proposed to
counteract the repressor protein (Stl) and promote SaPI excision
and transfer. A G protein-like mechanism was proposed which is
unexpected in light of the kinetic mechanism of dUTPase.
Here we investigate the molecular mechanism of SaPI transfer
regulation, using numerous dUTPase variants and a wide range
of in vitro methods (steady-state and transient kinetics, VIS and
fluorescence spectroscopy, EMSA, quartz crystal microbalance,
X-ray crystallography).
Our results unambiguously show that Stl inhibits the enzymatic
activity of dUTPase in the nM concentration range and
dUTP strongly inhibits the dUTPase: Stl complexation. These
results identify Stl as a highly potent dUTPase inhibitor protein
and disprove the G protein-like mechanism. Importantly, our
results clearly show that the dUTPase:dUTP complex is inaccessible
to the Stl repressor. Unlike in small GTPases, hydrolysis of
the substrate nucleoside triphosphate (dUTP in this case) is
required prior to the interaction with the partner (Stl repressor in
this case). We propose that dUTPase can efficiently interact with
Stl and induce SaPI excision only if the cellular dUTP level is low (i.e. when dUTPase resides mainly in the apo enzyme form)
while high dUTP levels would inhibit SaPI transfer. This mechanism
may serve the preservation of the integrity of the transferred
SaPI genes and links the well-known metabolic role of
dUTPases to their newly revealed regulatory function in spread
of virulence factors
Evolution of monogenetic rhyolite volcanoes: Vinicky, Eastern Slovakia
Four essential volcanic units have been recognized
in the late Middle Miocene rhyolite complex at
the southern side of the Zemplín horst next to the
village Viničky. A succession of ash/pumice flow,
surge and fall deposits separated by horizons of
eolian dust and paleosoil in total thickness >15
m forms the lower unit. It represents distal facies
deposits of subplinian/plinian/phreatoplinian type
eruptions at unidentified centers. The second
unit rests upon the lower one with unconformity
marking a
period of erosion.
It
consists of coarse
phreatic/phreatomagmatic pyroclastic rocks with
fragments of basement rocks and glassy dacite/
rhyodacite. They represent proximal facies of a
phreatomagmatic pyroclastic ring. Both units are
truncated by a rhyolite extrusive dome, formed
of perlite and perlitic breccias at its margin.
Emplacement of the dome concluded activity of
local centers northwest of Viničky. An extensive
rhyolite coulee represents the fourth, uppermost
volcanic unit. It is 40 – 70 m thick, formed of
felsitic rhyolite with perlite and perlitic breccia
at the base. Orientation of flow banding implies
that the Borsuk extrusive dome 1
km northeast
of Viničky was a source of the coulee. The dome
and coulee form together one rhyolite body of the
dome-flow type. With exception of the distal facies
tuffs at the base the rhyolite complex represents
most probably products of three overlapping
monogenetic volcanoe
Ground state of a partially melted Wigner molecule
We consider three spinless fermions free to move on 2d square lattice with
periodic boundary conditions and interacting via a U/r Coulomb repulsion. When
the Coulomb energy to kinetic energy ratio r_s is large, a rigid Wigner
molecule is formed. As r_s decreases, we show that melting proceeds via an
intermediate regime where a floppy two particle molecule coexists with a
partially delocalized particle. A simple ansatz is given to describe the ground
state of this mesoscopic solid-liquid regime.Comment: to appear in Europhysics Letter
Quantification of an atmospheric nucleation and growth process as a single source of aerosol particles in a city
Effects of a new aerosol particle formation (NPF) and particle diameter
growth process as a single source of atmospheric particle number
concentrations were evaluated and quantified on the basis of experimental
data sets obtained from particle number size distribution measurements in the
city centre and near-city background of Budapest for 5 years.
Nucleation strength factors for a nucleation day (NSFNUC) and for a
general day (NSFGEN) were derived separately for seasons and full
years. The former characteristic represents the concentration increment of
ultrafine (UF) particles specifically on nucleation days with respect to
accumulation-mode (regional background) concentrations (particles with
equivalent diameters of 100–1000 nm; N100−1000) due solely to the
nucleation process. The latter factor expresses the contribution of
nucleation to particle numbers on general days; thus, it represents a longer
time interval such as season or year. The nucleation source had the largest
effect on the concentrations around noon and early afternoon, as expected.
During this time interval, it became the major source of particles in the
near-city background. Nucleation increased the daily mean concentrations on
nucleation days by mean factors of 2.3 and 1.58 in the near-city background
and city centre, respectively. Its effect was largest in winter, which was
explained by the substantially lower N100−1000 levels on nucleation days
than those on non-nucleation days. On an annual timescale, 37 % of the UF
particles were generated by nucleation in the near-city background, while NPF
produced 13 % of UF particles in the city centre. The differences among
the annual mean values, and among the corresponding seasonal mean values,
were likely caused by the variability in controlling factors from year to
year. The values obtained represent the lower limits of the contributions.
The shares determined imply that NPF is a non-negligible or substantial
source of particles in near-city background environments and even in city
centres, where the vehicular road emissions usually prevail. Atmospheric
residence time of nucleation-mode particles was assessed by a decay curve
analysis, and a mean of 02:30 was obtained. The present study suggests that
the health-related consequences of the atmospheric NPF and growth process in
cities should also be considered in addition to its urban climate
implications
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