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A Director's Analysis of Luigi Pirandello's Henry IVMortensen, Virginia A. January 1964 (has links)
No description available.
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Characterization of interactions of the Type IV secretion system core component VirB8Sivanesan, Durga 09 1900 (has links)
<p> Type IV secretion systems (T4SS) are essential for the virulence of many gram-negative
pathogens. The systems studied here comprise eleven VirB proteins in case of
Agrobacterium tumefaciens and twelve in case of Brucella suis. The VirB proteins
associate in the cell envelope and form a complex that mediates the translocation of
virulence factors into host cells. In this report, VirB8, a core component of T4SS, is
characterized with regards to its interaction with itself and with other VirB proteins. </p> <p> VirB8 was found to exist in monomer-dimer equilibrium and the self-association
was demonstrated by analytical ultracentrifugation, analytical gel filtration, surface
plasmon resonance and bacterial two-hybrid assay. The above experiments demonstrated
that residues M102, Y105 and E214 o fVirB8 from B. suis are involved in self-association
and mutagenesis of these residues led to the impairment of T4SS function in B. suis.
Furthermore, this information was utilized to unravel the contribution of VirB8 self-association
towards T4SS assembly and function. To this end dimerization variants of
VirB8 from Agrobacterium tumefaciens were created and the effects were assessed with
purified proteins in vitro. Following this, the effects of VirB8 dimer site changes were
assessed in vivo. Introduction of a cysteine residue at the predicted interface (V97C)
supported DNA transfer but not T-pilus formation. Variants that reduced the self-association
did not support T4SS functions and T-pilus formation. Moreover, VirB2-
VirB5 co-fractionated with high molecular mass components from membranes of A.
tumefaciens and VirB8 dimerization was shown to be necessary for VirB2 association
with the high molecular mass components. Using purified VirB8 and VirB5 it was shown that VirB5 interacts with VirB8 via its globular domain and this interaction dissociates
VirB8 dimers. Taking these results together, a mechanistic contribution of VirB8
dimerization to T4SS assembly was proposed. </p> <p> Next, the interactions of VirB8 with other core components (VirB9 and VirBlO)
were analyzed by using various in vitro and in vivo experiments. Purified soluble
periplasmic domains of VirB8, VirB9 and VirB10 were used in enzyme-linked
immunosorbent assays, circular dichroism, and surface plasmon resonance experiments.
The pair-wise interactions and self-association of VirB8, VirB9 and VirB 10 were
demonstrated with the in vitro experiments. In addition, a ternary complex formation
between VirB8, VirB9, and VirBlO was identified. Using the bacterial two-hybrid
system, the dynamics of the interactions between VirB8-VirB9-VirB 10 full-length
proteins were analyzed demonstrating that VirB9 stimulates VirB8 self-association, but
that it inhibits the VirB10-VirB10 as well as the VirB8-VirB10 interaction. Based on
these results, a dynamic model for secretion system assembly is proposed where VirB8
plays a role as an assembly factor that is not closely associated with the functional core
complex comprising VirB9 and VirB10. </p> <p> The work reported in this thesis advances the understanding of VirB8 self-association
and its contribution to T4SS assembly and function. Furthermore, the
establishment of the bacterial two-hybrid system to detect VirB interactions has helped
identify inhibitors for the VirB8 dimerization through collaboration with Dr. Athanasios
Paschos. Moreover, techniques such as ELISA, analytical ultracentrifugation, circular dichroism and surface plasmon resonance will be utilized routinely to characterize other
VirB-VirB interactions in future. </p> / Thesis / Doctor of Philosophy (PhD)
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Studies on Hydrogen Sulfide Disposal Systems / A Preliminary Study of the Electrochemical Decomposition of Hydrogen Sulfide: The Determination of the Conductivity Displayed by H2s- Solute Mixtures / The Evaluation and Characterization of the Vanadium(IV) Species Present in Aqueous Solution Containing Citrate LigandWalker, Thomas 09 1900 (has links)
The following Thesis is comprised of two separate and individual
parts, both of which relate to the disposal of hydrogen
sulfide. Section One is an investigation into the possibility of
developing a hydrogen sulfide decomposition process which would
produce both hydrogen and elemental sulfur. Section Two deals with
the speciation study of a catalyst used in a traditional process
which converts hydrogen sulfide gas into elemental sulfur. / Section 1: <p> The disposal of hydrogen sulfide by electrolysis to produce
both hydrogen and sulfur appears to an interesting alternative to
the conventional Claus process which wastes the hydrogen content of
hydrogen sulfide. The electrolysis at room temperature has been
reported in the literature, however, the investigation was somewhat
limited by the low conductivity displayed by the electrolysis solution
(pyridine/hydrogen sulfide mixture). </p> <p> The primary goal of this research was to construct a suitable
apparatus and carry out a series of conductivity measurements of
liquid hydrogen sulfide at room temperature with and without the
addition of possible electrolytes. The objective was to determine if
an electrolyte could be found that would increase the conductivity
to a suitably high level to warrant the further investigation of the
electrolysis process. </p> <p> Of the six possible electrolytes, only tetrapropyl ammonium
iodide increased the conductivity to a desirable level. A 0.4034 M
solution of this alkyl ammonium iodide in liquid hydrogen sulfide
increased the conductivity (at 23 C) from 7.00 X 10-8 ohm-1cm-1 for
the pure solvent to 1.13 X 10-2 ohm-1cm-1. This increase was attributed
to the formation of the corresponding hydrogen sulfide adduct
and its subsequent dissociation in liquid hydrogen sulfide. </p> </p> Now that it has clearly been established that appropriately
high conducting solutions of hydrogen sulfide can be prepared, the
further investigation of the electrolysis of hydrogen sulfide as a
viable industrial process is warranted. </p> Section 2: <p> This section deals with the investigation of species present in
vanadium(IV): citrate solutions over a wide range of pH values.
Various spectroscopic methods (UV/VIS, ESR, vanadium Sl FT-NMR) were
used to probe this specific system. The accumulated spectroscopic data
were rationalized on the basis of thirteen vanadium(IV) containing
species, four of which were proposed to be vanadium(IV): citrate
species. Based on the observed spectroscopic data an equilibrium
diagram was prepared which illustrates the vanadium(IV) species present
as a function of pH. </p> / Thesis / Master of Science (MSc)
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The type IVa pilus machine is pre-installed during cell divisionCarter, Tyson January 2016 (has links)
Type IV pili (T4P) are protein filaments found on the surface of a variety of bacterial species and mediate biofilm formation, adhesion, and flagellum-independent twitching motility. The biogenesis of T4P is dependent on a cell envelope-spanning, multiprotein complex that localizes to the poles in rod-shaped cells. How these proteins localize and cross the peptidoglycan (PG) layer in the absence of dedicated PG-hydrolyzing enzymes is unknown. In P. aeruginosa, PilMNOP interact to form the alignment subcomplex, connected via PilP to PilQ, which forms the outer membrane secretin. We hypothesized that polar localization and integration of the T4P machinery was driven by ordered recruitment to future sites of cell division, placing assembly system components at division septa in the correct position before daughter-cell separation. To determine which T4P components are essential for localization of the complex, we fused the T4P inner membrane assembly protein PilO to the fluorescent protein mCherry to monitor its localization. mCherry-PilO localized to the cell poles and midcell in wild type bacteria. However, it was delocalized in a strain lacking PilQ. A PilQ-mCherry fusion localized to the cell poles, likely through its putative septal PG binding AmiN domains, suggesting that PilQ binds PG and thus localizes its partners to future sites of cell division. In the absence of the associated pilotin protein (PilF), which is required for PilQ multimerization in the OM, T4P components were polarly localized, implying that localization is not dependent on secretin formation. The results of this research support a pre-installation mechanism for integration of protein complexes in the gram negative cell envelope without PG hydrolysis, which may be applicable to other systems. / Thesis / Master of Science (MSc)
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Article IV: Confidentiality ProvisionsPearson, Graham S., Sims, N.A. January 2000 (has links)
Yes
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An Empire on the Brink of Destruction: The Stability of the Seleucid Empire Under Antiochus IV (175 B.C. - 164 B.C.)Campbell, Tyler 01 December 2014 (has links)
The Seleucid Empire expanded its territory to stretch from Thrace to India under the leadership of Antiochus III, making it one of the most expansive empires in the Hellenistic World. Antiochus III's subsequent loss at the Battle of Magnesia to Rome in 190 B.C. caused some of the satrapies of the empire to begin to rebel, and has led some historians to believe that the empire began an unrecoverable decline. In this investigation I will argue that the myth of decline in the post-Antiochus III era is invalid through analyzing the stability brought to the empire during the reign of his son, Antiochus IV. An investigation into Antiochus IV's stabilization of the Seleucid Empire has not been completed in English since 1966. Through analyzing his involvement in the southern and eastern regions of the Seleucid Empire as well as the internal reforms a clear picture of Antiochus IV's efforts towards stabilization becomes apparent.
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Discovery and demonstration of functional type IV pili production and post-translational modification by a medically relevant <i>Acinetobacter</i> speciesHarding, Christian Michael 21 May 2015 (has links)
No description available.
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The Role of Cellular Autophagy and Type IV Secretion System in <i>Anaplasma phagocytophilum</i> InfectionNiu, Hua 21 August 2008 (has links)
No description available.
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Single point mutations in type IV pilus fiber proteins restore twitching in ΔpilU mutantsBarnshaw, Rebecca 11 1900 (has links)
Type IV pili (T4P) are long adhesive surface filaments produced by bacteria and are a key virulence factor for many pathogens. T4P are produced by a dynamic intracellular nanomachine that facilitates the assembly (extension) and disassembly (retraction) of pili. Pilus dynamics are enabled by the motor subcomplex of the nanomachine, where cytoplasmic ATPases power pilus assembly (PilB) and disassembly (PilT and PilU). In many, but not all, T4P expressing bacteria – including our model organism Pseudomonas aeruginosa – two retraction ATPases are required for functional retraction, which can be assessed by measuring twitching motility. Deletion of pilT results in loss of twitching and phage susceptibility (another hallmark of pilus function) while deletion of pilU results in loss of twitching but retention of phage susceptibility, indicating pili can still be retracted. We hypothesized that PilU adds to the force of pilus retraction, facilitating disassembly when the fiber is under tension. We mutated ΔpilU and pilU::Tn5 strains with ethyl methanesulfonate and screened for gain-of-twitching mutants. Whole genome sequencing revealed multiple point mutations in the major pilin protein PilA or the pilus adhesin, PilY1. These point mutations were recapitulated in a ΔpilU strain and restored twitching to varying degrees. Complementation of pilA point mutants with pilU in trans influenced the twitching zone of only one mutant, and in trans expression of wild-type pilA resulted in a significant reduction in twitching in most. The contribution of PilU to the force of pilus retraction was further investigated by a polyacrylamide micropillar assay, where no pulling events could be detected for either ΔpilT or ΔpilU mutants. Exopolysaccharide production, a proxy for surface sensing, was uncoupled from twitching motility in the pilA point mutants. These results are a significant step forward to understanding what PilU does and, provides insight to the dynamics of the pilus fiber. / Thesis / Master of Science (MSc) / Pseudomonas aeruginosa is a bacterium that causes serious infections. P. aeruginosa uses adhesive, “grappling hook” filaments called Type IV pili (T4P) to stick to its hosts. T4P can be repeatedly extended and retracted, allowing the bacteria to crawl on surfaces (twitching) but making them susceptible to bacteriophages, viruses that attach to pili then kill the bacterial cells. The motor proteins PilT and PilU are required for twitching, but only PilT is essential for phage killing, implying that pili are retracted even when PilU is missing. Here we hypothesized that PilU is important for twitching because it helps generate force for retraction when pili are under tension. We isolated multiple mutations in pilus components that restored twitching in the absence of PilU, and propose that these mutations allow for easier retraction of pili. This information helps us understand how T4P help the bacteria to spread during infection.
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Characterization of the PilS-PilR two component regulatory system of Pseudomonas aeruginosaKilmury, Sara LN 11 1900 (has links)
Two-component regulatory systems are an important means for most prokaryotes to adapt quickly to changes in their environment. Canonical systems are composed of a sensor kinase, which detects signals that trigger autophosphorylation, and a response regulator, which imparts changes within the cell, usually through transcriptional regulation. The opportunistic pathogen, Pseudomonas aeruginosa, expresses a plethora of two-component systems including the PilS-PilR sensor-regulator pair, which directs transcription of the major component of the type IV pilus (T4P) system, pilA, in response to an unknown signal. T4P are surface appendages that are required for full virulence, as they perform several important functions including twitching motility, cell surface attachment, surface sensing, and biofilm formation. While loss of pili is known to decrease virulence, the effect of surplus surface pili on pathogenicity was unknown. In other T4P-expressing bacteria, PilR regulates the expression of non-T4P related genes, but its regulon in P. aeruginosa was undefined. Here, we identify PilA as an intramembrane signal for PilS, regulating its own expression. When PilS-PilR function is altered through the use of activating point mutations, which induce hyperpiliation, pathogenicity in C. elegans was significantly impaired compared to both wild type and non-piliated strains of P. aeruginosa. This phenotype could be recapitulated using other hyperpiliation-inducing mutations, providing evidence that over production of surface pili likely prevents productive engagement of contact-dependent virulence factors. Last, transcriptomic analyses revealed that expression of over 50 genes – including several involved in flagellar biosynthesis and function – is modulated by PilSR, suggesting coordinate regulation of motility in P. aeruginosa. Together, this work provides new information on the control of pilA transcription and suggests novel roles for surface pili and the PilSR two component system in virulence and swimming motility, respectively. The knowledge gained from this work could be applied to the development of a PilS or PilR based anti-virulence therapeutic. / Thesis / Doctor of Philosophy (PhD) / Pseudomonas aeruginosa is a Gram negative bacterium and a common cause of hospital acquired infections. The World Health Organization recently ranked P. aeruginosa as one of the top “priority pathogens” for which new treatments are desperately needed, in part due to its intrinsic resistance to many antibiotics. Among the key features that contribute to the infectivity of P. aeruginosa are its Type IV pili (T4P), which are flexible, retractile surface appendages involved in cell surface attachment, movement across solid surfaces and other important functions. Production of the major pilin protein, PilA, which forms most of the pilus, is tightly controlled by the two-component regulatory system, PilS-PilR, where PilS is a sensor and PilR is a regulator that directly controls pilin expression. The aim of this work was to identify the signal(s) detected by the sensor, as well as additional genes or systems under PilSR control. We showed that the pilin protein interacts directly with the sensor to control its own expression, and that dysregulation of the PilS-PilR two-component system impairs both pathogenicity and other forms of motility. Together, the data presented here provide insight into how PilS-PilR control expression of systems required for virulence of P. aeruginosa and highlight the potential of these proteins as possible therapeutic targets.
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