1,230 research outputs found
Thermoregulation of the \u3ci\u3epap\u3c/i\u3e Operon: Evidence for the Involvement of RimJ, the N-terminal Acetylase of Ribosomal Protein S5
Our previous work showed that pap pilin gene transcription is subject to a thermoregulatory control mechanism under which pap pilin is not transcribed at a low temperature (23°C) (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). In order to isolate genes involved in this temperature regulation of gene expression, chromosomal mini-TnlO (mTnlO) mutations that allowed transcription of the pap pilin gene at 23°C were identified, and the locus was designated tcp, for thermoregulatory control of pap (C. A. White-Ziegler, L. B. Blyn, B. A. Braaten, and D. A. Low, J. Bacteriol. 172:1775-1782, 1990). In the present study, quantitative analysis showed that the tcp mutations restore pap pilin transcription at 23°C to levels similar to those measured at 37°C. By in vivo recombination, the tcp mutations were mapped to phage E4H1OS of the Kohara library of the Escherichia coli chromosome (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987). The tcp locus was cloned by complementation, in which a 1.3-kb DNA fragment, derived from the Kohara phage, was shown to restore thermoregulation to the mTnlO mutants. DNA sequencing revealed two open reading frames (ORFs) encoding proteins with calculated molecular masses of 22.7 and 20.3 kDa. The sequence of the 22.7-kDa ORF was identical to that of rimJ, the N-terminal acetylase of the ribosomal protein S5. The gene encoding the 20.3-kDa ORF, designated g20.3 here, did not display significant homology to any known. DNA or protein sequence. On the basis of Northern (RNA) blot data, rimj and g20.3 are located within the same operon. Two of the mTnlO transposons in the thermoregulatory mutants were inserted within the coding region of rimi, indicating that the RimJ protein plays an important role in the temperature regulation ofpap pilin gene transcription. However, rimj itself is not thermoregulated, since rim. transcripts were detected at both 23 and 37°C. Disruption of the g20.3 gene by insertion and deletion mutagenesis did not affect thermoregulation of the pap operon, suggesting that, although g20.3 lies within the same operon as rimj, it does not play a role in thermoregulation
H-NS Controls \u3ci\u3epap\u3c/i\u3e and \u3ci\u3edaa\u3c/i\u3e Fimbrial Transcription in \u3ci\u3eEscherichia coli\u3c/i\u3e in Response to Multiple Environmental Cues
A comparative study was completed to determine the influence of various environmental stimuli on the transcription of three different fimbrial operons in Escherichia coli and to determine the role of the histone-like protein H-NS in this environmental regulation. The fimbrial operons studied included the pap operon, which encodes pyelonephritis-associated pili (P pili), the daa operon, which encodes F1845 fimbriae, and the fan operon, which encodes K99 fimbriae. Using lacZYA transcriptional fusions within each of the fimbrial operons, we tested temperature, osmolarity, carbon source, rich medium, oxygen levels, pH, amino acids, solid medium, and iron concentration for their effects on fimbrial gene expression. Low temperature, high osmolarity, glucose as a carbon source, and rich medium repressed transcription of all three operons. High iron did not alter transcription of any of the operons tested, whereas the remaining stimuli had effects on individual operons. For the pap and daa operons, introduction of the hns651 mutation relieved the repression, either fully or partially, due to low temperature, glucose as a carbon source, rich medium, and high osmolarity. Taken together, these data indicate that there are common environmental cues that regulate fimbrial transcription in E. coli and that H-NS is an important environmental regulator for fimbrial transcription in response to several stimuli
Identification of an \u3ci\u3eEscherichia coli\u3c/i\u3e Genetic Locus Involved in Thermoregulation of the \u3ci\u3epap\u3c/i\u3e Operon
We previously showed, using a single-copy papBAp-lac fusion (previously designated papBA-lac), that pyelonephritis-associated pili (pap) pilin gene transcription is subject to both phase variation and thermoreg- ulatory control mechanisms (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). At 37°C, Escherichia coli strains carrying the papBAp-lac fusion displayed both Lac\u27 and Lac- colony phenotypes. In contrast, at 23°C, colonies displayed a uniform Lac- phenotype, suggesting that pilin was not transcribed at this temperature. In this study, a strain carrying the papBAp-lac fusion was subjected to mini-TnlO (mTnlO) mutagenesis to isolate mutants that could initiate transcription of pilin at the nonpermissive temperature. Two classes of thermoregulatory mutants were identified in which the mTnlO mutation was linked to the mutant phenotype. Class I mutants displayed a phase variation phenotype at both 37°C and 23°C, whereas class II mutants displayed a uniform Lac\u27 colony phenotype at both temperatures. Preliminary analysis of these mutants showed that the mTnlO insertions in the class I mutants were chromosomally located, whereas the mTnlO insertions in the class II mutants were located within the papBAp-lac fusion phage. Southern blot analysis of the class I mutants demonstrated that mTnlO was present in the same 5.9-kilobase Sall DNA fragment in each mutant. Two of the class I mTnlO mutations were mapped to approximately 23.4 min on the E. coli K-12 chromosome. The locus defined by the class I mTnlO mutations was designated tcp, for thermoregulatory control ofpap. Analysis of phase transition rates of the class I mutants showed that the phase-off (Lac-)\u3e phase-on (Lac\u27) transition rates were higher than those observed with the nonmutant E. coli strain
Phase-Variation of Pyelonephritis-Associated Pili in \u3ci\u3eEscherichia coli\u3c/i\u3e: Evidence for Transcriptional Regulation
The regulation of pyelonephritis-associated pill (pap) pflin gene transcription has been examined using two operons (pap-17 and pap-21) isolated from the pyelonephritogenic Escherichia coli strain C1212. DNA sequence analysis and E.coli minicell analysis were used to map two genes (papB and papl) within the pilin regulatory regions of both pap-17 and pap-21, and the protein products of these genes were identified. Pilin transcription, initiated at the papBA promoter, was monitored by constructing single copy operon fusions with lacZYA in E.coli K-12. Inocula- tion of E.coli (pap\u27-lac) strains onto solid M9 minimal medium containing glycerol and the Lac indicator X-gal (M9-Glycerol) yielded both Lac\u27 and Lac- colony phenotypes. The Lac\u27 (\u27phase on\u27) and Lac- (\u27phase off\u27) phenotypes were heritable since reinoculation of M9-Glycerol with bacteria picked from Lac\u27 colonies gave rise to a much higher fraction of Lac\u27 colonies than reinoculation of M9-Glycerol with bacteria picked from Lac- colonies. Measurement of phase transition rates for E.coli (pap17\u27-lac) inoculated onto M9-Gly- cerol showed that the Lac - -Lac+ transition frequency (1.57 x 10-4/cell/generation) was reduced 35-fold when cells were inoculated onto minimal medium containing glucose (M9-Glucose). However, the Lac+-Lac- transition frequency obtained using M9-Glycerol (2.60 x 10-2/cell/generation) was 1.4-fold lower compared to results obtained with M9-Glucose. In contrast, lowering the incubation temperature of E.coli (pap17\u27-lac) cultures from 37°C to 23\u27C caused all cells to shift to the Lac- state. Together, our results strongly indicate that pap pfli phase-variation is transcriptionally regulated and show that phase-variation is responsive to changes in the bacterial environment
Offsetting Versus Mitigation Activities to Reduce CO2 Emissions: A Theoretical and Empirical Analysis for the U.S. And Germany
New insights into the structure of early-type galaxies: the Photometric Plane at z~0.3
We study the Photometric Plane (PHP), namely the relation between the
effective radius re, the mean surface brightness within that radius e, and
the Sersic index n, in optical (R and I) and near-infrared (K) bands for a
large sample of early-type galaxies (ETGs) in the rich cluster MS1008-1224 at
z=0.306. The PHP relation has an intrinsic dispersion of ~32% in re, and turns
out to be independent of waveband. This result is consistent with the fact that
internal colour gradients of ETGs can have only a mild dependence on galaxy
luminosity (mass). There is no evidence for a significant curvature in the PHP.
We show that this can be explained if this relation origins from a systematic
variation of the specific entropy of ETGs along the galaxy sequence, as was
suggested from previous works. The intrinsic scatter of the PHP is
significantly smaller than for other purely photometric relations, such as the
Kormendy relation and the photometric Fundamental Plane, which is constructed
by using colours in place of velocity dispersions. The scatter does not depend
on the waveband and the residuals about the plane do not correlate with
residuals of the colour-magnitude relation. Finally, we compare the
coefficients of the PHP at z~0.3 with those of ETGs at z~0, showing that the
PHP is a valuable tool to constrain the luminosity evolution of ETGs with
redshift. The slopes of the PHP do not change significantly with redshift,
while the zero-point is consistent with cosmological dimming of the surface
brightness in an expanding universe plus the passive fading of galaxy stellar
populations with a high formation redshift (z_f >1-2).Comment: 21 pages, 10 figures, MNRAS in pres
Accurate ab initio spin densities
We present an approach for the calculation of spin density distributions for
molecules that require very large active spaces for a qualitatively correct
description of their electronic structure. Our approach is based on the
density-matrix renormalization group (DMRG) algorithm to calculate the spin
density matrix elements as basic quantity for the spatially resolved spin
density distribution. The spin density matrix elements are directly determined
from the second-quantized elementary operators optimized by the DMRG algorithm.
As an analytic convergence criterion for the spin density distribution, we
employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.
2011, 134, 224101] to build an accurate complete-active-space
configuration-interaction (CASCI) wave function from the optimized matrix
product states. The spin density matrix elements can then also be determined as
an expectation value employing the reconstructed wave function expansion.
Furthermore, the explicit reconstruction of a CASCI-type wave function provides
insights into chemically interesting features of the molecule under study such
as the distribution of - and -electrons in terms of Slater
determinants, CI coefficients, and natural orbitals. The methodology is applied
to an iron nitrosyl complex which we have identified as a challenging system
for standard approaches [J. Chem. Theory Comput. 2011, 7, 2740].Comment: 37 pages, 13 figure
Joint Cosmological Formation of QSOs and Bulge-dominated Galaxies
Older and more recent pieces of observational evidence suggest a strong
connection between QSOs and galaxies; in particular, the recently discovered
correlation between black hole and galactic bulge masses suggests that QSO
activity is directly connected to the formation of galactic bulges. The
cosmological problem of QSO formation is analyzed in the framework of an
analytical model for galaxy formation; for the first time a joint comparison
with galaxy and QSO observables is performed. In this model it is assumed that
the same physical variable which determines galaxy morphology is able to
modulate the mass of the black hole responsible for QSO activity. Both halo
spin and the occurence of a major merger are considered as candidates to this
role. The predictions of the model are compared to available data for the
type-dependent galaxy mass functions, the star-formation history of elliptical
galaxies, the QSO luminosity function and its evolution (including the obscured
objects contributing to the hard-X-ray background), the mass function of
dormant black holes and the distribution of black-hole -- bulge mass ratios. A
good agreement with observations is obtained if the halo spin modulates the
efficiency of black-hole formation, and if the galactic halos at have
shone in an inverted order with respect to the hierarchical one (i.e., stars
and black holes in bigger galactic halos have formed before those in smaller
ones). This inversion of hierarchical order for galaxy formation, which
reconciles galaxy formation with QSO evolution, is consistent with many pieces
of observational evidence.Comment: 20 pages, figures included, mn.sty, in press on MNRAS, fig 6 changed
(new data added at z=4.4
Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3
Context. Recently, the high-energy (HE, 0.1-100 GeV) -ray emission
from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered
to be modulated with a 10.3-day period, making it the first extra-galactic
-ray binary.
Aims. This work aims at the detection of very-high-energy (VHE, >100 GeV)
-ray emission and the search for modulation of the VHE signal with the
orbital period of the binary system.
Methods. LMC P3 has been observed with the High Energy Stereoscopic System
(H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has
been folded with the known orbital period of the system in order to test for
variability of the emission. Energy spectra are obtained for the orbit-averaged
data set, and for the orbital phase bin around the VHE maximum.
Results. VHE -ray emission is detected with a statistical
significance of 6.4 . The data clearly show variability which is
phase-locked to the orbital period of the system. Periodicity cannot be deduced
from the H.E.S.S. data set alone. The orbit-averaged luminosity in the
TeV energy range is erg/s. A luminosity of erg/s is reached during 20% of the orbit. HE and VHE
-ray emissions are anti-correlated. LMC P3 is the most luminous
-ray binary known so far.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&
Recommended from our members
Measurement of B(B-->X_s {\gamma}), the B-->X_s {\gamma} photon energy spectrum, and the direct CP asymmetry in B-->X_{s+d} {\gamma} decays
The photon spectrum in B --> X_s {\gamma} decay, where X_s is any strange
hadronic state, is studied using a data sample of (382.8\pm 4.2) \times 10^6
e^+ e^- --> \Upsilon(4S) --> BBbar events collected by the BABAR experiment at
the PEP-II collider. The spectrum is used to measure the branching fraction B(B
--> X_s \gamma) = (3.21 \pm 0.15 \pm 0.29 \pm 0.08)\times 10^{-4} and the
first, second, and third moments = 2.267 \pm 0.019 \pm 0.032 \pm
0.003 GeV,, )^2> = 0.0484 \pm 0.0053 \pm 0.0077 \pm
0.0005 GeV^2, and )^3> = -0.0048 \pm 0.0011 \pm 0.0011
\pm 0.0004 GeV^3, for the range E_\gamma > 1.8 GeV, where E_{\gamma} is the
photon energy in the B-meson rest frame. Results are also presented for
narrower E_{\gamma} ranges. In addition, the direct CP asymmetry A_{CP}(B -->
X_{s+d} \gamma) is measured to be 0.057 \pm 0.063. The spectrum itself is also
unfolded to the B-meson rest frame; that is the frame in which theoretical
predictions for its shape are made.Comment: 37 pages, 19 postscript figures, submitted to Phys. Rev. D. No
analysis or results have changed from previous version. Some changes to
improve clarity based on interactions with Phys. Rev. D referees, including
one new Figure (Fig. 13), and some minor wording/punctuation/spelling
mistakes fixe
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