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Biomedical subjects

A Wright

Publications and source records attributed to A Wright.

At least 307 records · Page 17Linked to original sources
PubMed1986

Enhancement of bacterial gene expression by insertion elements or by mutation in a CAP-cAMP binding site.

The regulatory region (bglR) of the cryptic bgl operon was characterized by DNA sequence analysis and transcription mapping. Bgl(-)-specific transcription was found to occur in both the wild-type Bgl- and mutant Bgl+ cells. However, the steady-state level of bgl RNA was much higher in the Bgl+ mutant than in the wild-type. Activation of the bgl operon by insertion sequence-mediated bglR mutations or point mutations in bglR is therefore the result of increased transcription. The ethylmethane sulfonate-induced point mutations in bglR are alterations in a single base in the cAMP binding protein (CAP) binding site, leading to a stronger binding of the CAP-cAMP complex. The IS1 and IS5-mediated bglR mutations analyzed show that the insertion sequences can activate the bgl operon by integration 78 to 125 base-pairs upstream from the transcription initiation site. The role of the insertion sequences in activation of the bgl operon is discussed.

Base Sequence↗
PubMed1986

Inactivation of rat brain acetylcholinesterase by pyridoxal 5'-phosphate.

Effects of pyridoxal 5'-phosphate on the activity of crude and purified acetylcholinesterase from cerebral hemispheres of adult rat brain were examined. Acetylcholinesterase was completely inactivated by incubation with 0.5 mM pyridoxal 5'-phosphate. The enzyme activity remained unaltered in the presence of analogs of pyridoxal 5'-phosphate, pyridoxal, pyridoxamine and pyridoxamine 5'-phosphate. The inhibition of acetylcholinesterase activity by pyridoxal 5'-phosphate appeared to be of a noncompetitive nature, as determined by Lineweaver-Burk analysis. The inhibitory effect of pyridoxal 5'-phosphate on acetylcholinesterase appeared to be a general one, as the activity of the enzyme from the brains of immature chick and egg-laying hen, and from different tissues of the adult male rats, exhibited a similar pattern in the presence of the inhibitor. The inhibitory effects of pyridoxal 5'-phosphate could be reversed upon exhaustive dialysis of the pyridoxal 5'-phosphate-treated acetylcholinesterase preparations. We propose that the effects of pyridoxal 5'-phosphate are due to its interaction with acetylcholinesterase, and that it can be employed as a useful tool for studying biochemical aspects of this important brain enzyme.

Acetylcholinesterase↗
PubMed1986

The in vitro cytotoxicity of asbestos fibers: I. P388D1 cells.

In this study, the cytotoxicity of 13 fibrous samples of known fiber number and dimensions has been established in P388D1 cells. The cells were exposed in vitro to dust concentrations of 10 or 50 micrograms/ml and, after incubation for 24 or 48 hours, any changes in cellular viability, lactate dehydrogenase, and glucosaminidase levels were determined. In general, there was a close association between the reduction in cellular viability and the loss of intracellular enzymes induced by each dust, the chrysotile asbestos samples proving more cytotoxic than the amphiboles. The cytotoxicity of the fibrous dusts was shown to be related to the number of fibers greater than 8 micron in length in the samples.

Animals↗
PubMed1986

DNA methylation differentially enhances the expression of one of the two E. coli dnaA promoters in vivo and in vitro.

The promoter/regulatory region of the dnaA gene, whose gene product is required for the initiation of DNA replication in Escherichia coli K-12, contains an unusually large number of Dam methylation sites. In this paper we report that the expression of the dnaA gene is decreased in Dam- strains of E. coli. The decrease in the expression of dnaA was measured in vivo using a dnaA-lacZ gene fusion. In vivo S1 nuclease mapping demonstrated that the decrease was due to a differential decrease in expression from the more proximal of the two dnaA promoters, dnaA2P. Comparison of the strengths of the two dnaA promoters in an in vitro transcription system using methylated and unmethylated DNA templates suggests that the effect of methylation on dnaA2P is probably at the level of RNA polymerase/DNA interaction. We suggest that this effect of methylation may be important in controlling the expression of dnaA during the E. coli cell cycle.

Bacterial Proteins↗
PubMed1986

Vectors for the construction of gene banks and the integration of cloned genes in Schizosaccharomyces pombe and Saccharomyces cerevisiae.

We have constructed a variety of vectors for use in both budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe). Four of these, pDB262, pWH4, pWH5, and pMAK262, have positive selection for the insertion of cloned DNA, making them convenient for the construction of gene banks. pDB262, pWH4 and pWH5 contain the 2 mu ARS and the LEU2 gene from S. cerevisiae and can be used for gene isolation. They can also be converted into integration vectors for use in the genetic mapping of cloned sequences. pMAK262 contains only the LEU2 gene from budding yeast and can be used to screen for ARS elements or for gene integration. We also describe two other integration vectors, pDAM3 and pDAM6, which have a variety of restriction sites suitable for subcloning.

Chromosome Mapping↗
PubMed1986

Effects of the inhalation of dusts from calcium silicate insulation materials in laboratory rats.

The effects of respirable dust from three commercially produced calcium silicate insulation materials were examined in laboratory rats by long-term inhalation and injection techniques. These calcium silicate products have been used as replacements for asbestos in the insulation of the engine rooms of ships, and the particle size distribution of the dust clouds generated for the experimental study closely matched those found in ships during the installation of this type of material. One year of exposure to a dust cloud of 10 mg/m3 of respirable dust had no discernible effect on the length of survival of treated animals compared to controls. No pulmonary lesions were found that appeared associated with the inhalation of calcium silicate per se, but one sample did contain significant amounts of quartz and this did produce a few small pulmonary nodules. While two small pulmonary neoplasms, one malignant and one benign, were found in dusted animals, neither was the cause of death, and the incidence was not significantly different from the control group where no tumors were found. One peritoneal mesothelioma was found in an animal from one of the inhalation groups, but this was considered to be a spontaneous tumor as none of over 100 animals injected intraperitoneally with 25 mg of calcium silicate developed these tumors. While the white blood cell count of dusted animals, compared to controls, was significantly raised in all treated groups at the end of the dusting period, these figures were within the published normal ranges for laboratory rats. It was concluded that the three tested calcium silicate products were harmless to the rats of this species at the doses tested.

Animals↗
PubMed1986

An improved morphological technique for the study of cochleotoxicity in guinea pigs.

Scanning electron microscopy is commonly used to study the normal or pathologically altered cochlear epithelium. It is especially useful for the study of ototoxicity in humans or animals. A cochlear microdissection technique in the guinea pig is presented which permits examination of the whole membranous cochlea with little artefactual damage to the sensory structures under study.

Animals↗
PubMed1986

Pathogenesis of IgA1 protease-producing and -nonproducing Haemophilus influenzae in human nasopharyngeal organ cultures.

We evaluated mucosal attachment, colonization, and invasion by Haemophilus influenzae in an experimental model of human nasopharyngeal tissue in organ culture. Nonpiliated, encapsulated, and nonencapsulated, IgA1 protease-deficient mutants of H. influenzae were compared with their isogenic IgA1 protease-producing parents. Damage to peripheral ciliary activity was first noted 6 hr after infection and was associated with sloughing of ciliated cells to which H. influenzae were not attached. Infection of organ cultures with each strain resulted in similar degrees and rates of ciliary damage. H. influenzae attached selectively to nonciliated epithelial cells or was associated with surface mucus. Later, disruption of epithelial tight junctions was observed, and clusters of H. influenzae were found between epithelial cells. Organisms were also seen within phagocytic vacuoles of mononuclear cells located above and below the basement membrane. In summary, encapsulated and nonencapsulated H. influenzae damaged the ciliary function of human nasopharyngeal organ cultures, attached to the mucosal surface, and invaded the epithelium. H. influenzae IgA1 protease, however, was not essential for the pathogenic steps observed in this human nasopharyngeal organ culture model.

Haemophilus Infections↗
PubMed1986

Inner hair cell loss and intracochlear clot in the preterm infant.

Little is known about the pathological changes in the cochlea of preterm infants which might be responsible for the hearing loss which the infants are at risk of developing. This study looks at the cochleas of 5 preterm infants who died at ages up to 2 weeks using light and electronmicroscopic techniques, and shows changes in the inner hair cell population in association with intracochlear clot which may be responsible for subsequent hearing loss.

Cerebral Hemorrhage↗
PubMed1986

Cerebrospinal fluid pulsation: benefits and pitfalls in MR imaging.

Physiologic cerebrospinal fluid (CSF) pulsation causes a harmonic modulation of proton precessional phase with two-dimensional Fourier transform (2DFT) imaging, which results in predictable regions of signal loss and the presence of phase-shift images ("ghost images"). CSF that is not pulsating exhibits a higher signal than does pulsatile CSF. This phenomenon can be diagnostically useful in disease entities associated with decreased CSF pulsation amplitude, such as arachnoid cyst, intraventricular cyst, spinal stenosis, and spinal block caused by extramedullary or epidural tumor. Unfortunately, this increased signal can also mimic disease such as epidural tumor in the spine or acoustic neuroma in the internal auditory canal. An abnormal pattern of CSF pulsation, as occurs in patients with arachnoiditis, can cause unusual areas of signal loss, which complicate image interpretation and can mimic pathologic conditions. Recognition of CSF pulsation effects will increase in importance as thin-section magnetic resonance imaging becomes more common, because thin sections enhance these effects with 2DFT.

Central Nervous System Diseases↗
PubMed1986

Physiologic growth and development of the lung during the first year of life.

Pulmonary function tests were performed on a total of 125 healthy infants younger than 25 postconception (pc) months of age. Maximal expiratory flow at functional residual capacity (VmaxFRC) was measured from partial expiratory flow-volume curves, and functional residual capacity (FRC) was measured by the helium dilution technique. There was a highly significant (p less than 0.01) linear regression for both VmaxFRC and FRC with increasing body length. The highest size-corrected flows (VmaxFRC/FRC) were obtained in the healthy premature (2.7 FRC/s, n = 6) and full-term (2.5 FRC/s, n = 5) infants, and there was a relatively constant value between 13 and 25 pc months of age (1.2 FRC/s), which was similar to those reported in older children and adults. In an age-matched group of infants 10 to 16 pc months of age, females had both higher absolute flows (126 versus 102 ml/s, p less than 0.03) and size-corrected flows (1.4 versus 1.0 FRC/s, p less than 0.001) than did males. These physiologic data support the concepts that neonates have proportionately larger airways relative to their lung volume at FRC, infants have size-corrected flows similar to those in older children and adults, and female infants have proportionately larger airways relative to their lung size than do male infants.

Chloral Hydrate↗
PubMed1985

Use of transdermal glyceryl trinitrate to reduce failure of intravenous infusion due to phlebitis and extravasation.

Self-adhesive patches which release glyceryl trinitrate at a slow continuous rate or placebo patches were applied to the skin of patients distal to intravenous infusion sites in a double-blind manner. The frequency of infusion failure was three times lower with the glyceryl trinitrate than with placebo patches. The decrease was of similar magnitude whether failure was due to extravasation or phlebitis. Headaches were more common in patients with active patches but were relieved by simple analgesics.

Administration, Topical↗
PubMed1985

Autoregulation of the DNA replication gene dnaA in E. coli K-12.

The dnaA gene in E. coli K-12 is required for the initiation of DNA replication. Although the specific function of the dnaA protein is unknown, it has been suggested that it is a regulator of the frequency of initiation. In this paper we report that the expression of both a dnaA-lacZ translational fusion and a dnaA-trpA-lacZ transcriptional fusion in vivo are sensitive to changes in the level of functional dnaA protein. Overproduction of the dnaA gene product leads to a reduction in expression from both fusions while introduction of dnaA- alleles results in an increased expression. Results from a deletion analysis of the dnaA promoter/regulatory region suggest that both dnaA promoters are regulated by the dnaA gene product and that a site between the two promoters is responsible for the regulation. DNAase protection experiments showed that the dnaA protein binds to DNA in the region of the two dnaA promoters. Our results indicate that the dnaA gene product regulates its own synthesis by inhibiting transcription from both of its promoters.

Bacterial Proteins↗
PubMed1985

Fusions of secreted proteins to alkaline phosphatase: an approach for studying protein secretion.

We have constructed a series of plasmids containing a modified form of the phoA gene of Escherichia coli K-12 that have general utility for studies of protein secretion. In these plasmids, the promoter and signal sequence-encoding region of the phoA gene have been deleted; thus, expression of the gene, giving rise to active alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1], is absolutely dependent upon fusion in the correct reading frame to DNA containing a promoter, a translational start site, and a complete signal sequence-encoding region. Alkaline phosphatase, which is normally located in the periplasm of E. coli, is efficiently secreted to the periplasm when fused either to a signal sequence from another periplasmic protein, beta-lactamase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6), or to signal sequences from the outer membrane proteins LamB and OmpF. These heterologous signal sequences are processed during secretion. In the absence of a complete signal sequence, phosphatase becomes localized in the cytoplasm and is inactive. Phosphatase fusion proteins lacking up to 13 amino-terminal amino acids beyond the signal sequence show the same specific activity as that of the wild-type enzyme. However, a significant decrease in activity is seen when 39 or more amino-terminal amino acids are deleted. Addition of approximately 150 amino acids from the enzyme beta-lactamase to the amino terminus of alkaline phosphatase has little effect on the specific activity of the enzyme. The ability to change the amino terminus of phosphatase without altering its activity makes the enzyme particularly useful for construction of protein fusions. The fact that phosphatase is designed for transport across the cytoplasmic membrane makes it an ideal tool for study of protein secretion.

Alkaline Phosphatase↗