PubMed Health⌕ Search

Biomedical subjects

B Sheehan

Publications and source records attributed to B Sheehan.

9 recordsLinked to original sources
PubMed1996

A single substitution in the putative helix-turn-helix motif of the pleiotropic activator PrfA attenuates Listeria monocytogenes virulence.

PrfA, the regulator of virulence-gene expression in the pathogenic bacterium Listeria monocytogenes, displays sequence similarity to members of the CAP-FNR family of transcriptional regulators. To test the functional significance of this similarity, we constructed and analysed substitutions of two amino acids of PrfA predicted to contact DNA, i.e. Ser-184 and Ser-183. Substitution of Ser-184 by Ala reduced DNA binding and virulence-gene activation, and attenuated the virulence in a mouse model of infection. In contrast, substitution of Ser-183 by Ala had the opposite effect in these functional assays. A 17bp DNA sequence, which includes a putative PrfA site, was shown to be sufficient for target-site recognition by PrfA and PrfA-S183A. Our results strongly support the hypothesis that PrfA is a structural and functional homologue of CAP. In addition, they establish a clear correlation between DNA binding by PrfA, virulence-gene activation, and virulence.

Amino Acid Sequence↗
PubMed1995

Differential activation of virulence gene expression by PrfA, the Listeria monocytogenes virulence regulator.

PrfA is a pleiotropic activator of virulence gene expression in the pathogenic bacterium Listeria monocytogenes. Several lines of evidence have suggested that a hierarchy of virulence gene activation by PrfA exists. This hypothesis was investigated by assessing the ability of PrfA to activate the expression of virulence gene fusions to lacZ in Bacillus subtilis. Expression of PrfA in this heterologous host was sufficient for activation of transcription at the hly, plcA, mpl, and actA promoters. Activation was most efficient at the divergently transcribed hly and plcA promoters. The putative PrfA binding site shared by these promoters is perfectly symmetrical and appears to represent the optimum sequence for target gene activation by PrfA. The activation of actA and mpl expression was considerably weaker and occurred more slowly than that observed at the hly and plcA promoters, suggesting that greater quantities of PrfA are required for productive interaction at these promoters. Interestingly, expression of an inlA-lacZ transcriptional fusion was very poorly activated by PrfA in B. subtilis, suggesting that other Listeria factors, in addition to PrfA, are required for PrfA-mediated activation at this promoter. Further support for the involvement of such factors was obtained by constructing and analyzing a prfA deletion mutant of L. monocytogenes. We observed that, in contrast to that of the other genes of the PrfA regulon, expression of inlA is only partially dependent on PrfA.

Animals↗
PubMed1978

Effects of intravenous vasopressin on canine mesenteric arterial blood flow, bowel oxygen consumption, and cardiac output.

The effects of various doses of intravenous vasopressin on mesenteric arterial blood flow, intestinal oxygen consumption, and cardiac output in anesthetized dogs were investigated. Optimal dose rate of intravenous vasopressin was found to be 3.0 mU/kg/min. At this dose rate, mesenteric arterial blood flow, intestinal oxygen consumption, and cardiac output decreased by 57%, 57% and 26%, respectively. Increasing the dose rate to 8.0 mU/kg/min did not offer significant gains. Maximum effect was observed 20 min after the beginning of the infusion. The effects disappeared 10-20 min after the infusion was discontinued, with the exception of superior mesenteric blood flow which showed a rebound increase. We conclude that in the anesthetized dog, intravenous infusions of vasopressin at low dose rates (3.0 mU/kg/min) substantially reduce mesenteric blood flow and intestinal oxygen extraction with moderate reduction of cardiac output. Possible clinical applications of low dose intravenous infusions of vasopressin would include reduction of portal hypertension and bowel protection during radiation therapy.

Animals↗
PubMedDate not supplied

AVS software for visualization in molecular microscopy.

AVS (Application Visualization System) is commercially available software for analyzing and viewing data. AVS is primarily used in the physical sciences and engineering, and here we describe the application of AVS for examining three-dimensional density maps generated by electron microscopy and image processing. For this purpose, AVS can be applied with relative ease, even though the software is indeed quite sophisticated. The primary advantage is that visualization applications can be generated by combining software components, called modules, into executable flow networks. Simple networks are described for generating ribbon diagrams of macromolecules, surface-shaded views, and contour maps. Easy to use dials, bar sliders, and buttons provide tremendous versatility for real-time manipulation of isosurface values, depth cueing, view orientation, size, and animation. In addition, AVS supplies a framework for building new modules in C or FORTRAN. Modules for excavation and cropping provide tools that are particularly useful for extracting segments of a map and for examining maps of supramolecular complexes such as viruses. We describe a number of modules we have designed for analysis of three-dimensional data sets, as well as modules for importing image data from other software packages into AVS. We also describe xformat, a stand-alone file conversion utility designed to allow import of a variety of image and map file formats into AVS.

Capsid↗