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Biomedical subjects

W Walter

Publications and source records attributed to W Walter.

At least 19 recordsLinked to original sources
PubMed1990

DnaK, DnaJ, and GrpE heat shock proteins negatively regulate heat shock gene expression by controlling the synthesis and stability of sigma 32.

The Escherichia coli DnaK heat shock protein has been identified previously as a negative regulator of E. coli heat shock gene expression. We report that two other heat shock proteins, DnaJ and GrpE, are also involved in the negative regulation of heat shock gene expression. Strains carrying defective dnaK, dnaJ, or grpE alleles have enhanced synthesis of heat shock proteins at low temperature and fail to shut off the heat shock response after shift to high temperature. These regulatory defects are due to the loss of normal control over the synthesis and stability of sigma 32, the alternate RNA polymerase sigma-factor required for heat shock gene expression. We conclude that DnaK, DnaJ, and GrpE regulate the concentration of sigma 32. We suggest that the synthesis of heat shock proteins is controlled by a homeostatic mechanism linking the function of heat shock proteins to the concentration of sigma 32.

Alleles↗
PubMed1990

[Shielded vaginal applicators for line-shaped 192Ir sources for use in the irradiation of cervix cancer].

The possibility is investigated to use shielded vaginal applicators for "line-shaped" 192Ir-sources to irradiate cervical carcinoma. Using segment-shaped absorbers of heavy metal the dose can be reduced in ventro-dorsal direction in area of rectum and bladder with irradiation of cervical carcinoma up to a factor of 2 in dependence of rectum and bladder position. Selecting a suitable source position and source standing time a dose reduction can be realized in cranial direction up to two centimetres from the portio.

Brachytherapy↗
PubMed1989

Degenerative and regenerative processes in the peripheral nerve after disconnection and reanastomosis using the Neodym Yag laser.

The development of neuroma after peripheral nerve surgery is still an unsolved problem. Such lesions are not yet controllable by conventional methods. Reports of results achieved using various types of laser surgery appear contradictory. In this experimental study on rats, the Neodym Yag laser was found to be superior the conventional methods. After severance and reanastomosis of the sciatic nerve using this type of laser, no development of neuroma was observed in any of the animals during the first three months of observation.

Animals↗
PubMed1989

[Possibilities of isodose distribution in afterloading contact therapy of non-operated uterine cancer using an applicator tube and a point-shaped radiation source].

For the contact radiotherapy according to the afterloading-procedure of patients with cervical and endometrial carcinomas isodose plans are represented, that are standardized to the lengths of uterus probes and adapted to tumor stages and are determined by an applicator tube lying centrally within the uterine cavity. By an additional lead screening of the vaginal applicator a dose reduction can be attained by the factor 1.6 or 1.4 in the critical organs bladder and rectum, which are relevant for this therapeutic form. An uncritical inclusion of the vagina into the target volume of contact therapy, that is not justified by tumor invasion, should not be carried out, knowing the higher complication rate at the critical organs.

Brachytherapy↗
PubMed1989

[Dosimetric studies of 192Ir line sources and the mathematical presentation of the dose distribution].

The dose distribution of a "line-shaped" 192Ir-source was measured in 1,152 measuring points in a water phantom. Using regression analysis the analytical description of dose distribution was obtained. Accomplished comparison measurings with a solid phantom of miramide in 45 measuring points show that the dose distribution can be reproduced well by solid phantom measurings. Taking an ideal line source distribution as a basis, the r-dependence of correction factor, obtained by regression analysis, refers to a dispersion effect. The angle-dependent deviation of dose distribution from the ideal line source can be described by cos-terms with the single and double angle between line source axis and measuring point.

Brachytherapy↗
PubMed1989

[A comparison between the dose distribution from 192Ir point and line sources in the afterloading therapy of gynecologic neoplasms].

For different fields of application in irradiation of gynecological tumors a comparison of isodose distribution is done with "point-shaped" and "line-shaped" 192Ir-source. With the oblateness of dose efficiency distribution towards the axis of source with the "line-shaped" 192Ir-source an improvement of dose distribution occurs in intracavitary irradiation with the lower and more balanced exposure of fundus uteri, especially in irradiation of the endometrial carcinoma. On the other hand the irradiation of vaginal stump renders problematic. In pure vaginal irradiation no differences are found in medically interesting range.

Brachytherapy↗
PubMed1984

Effects of the mutant sigma allele rpoD800 on the synthesis of specific macromolecular components of the Escherichia coli K12 cell.

Escherichia coli K12 strains containing the mutant sigma allele rpoD800 are temperature-sensitive for growth. We have compared gene expression in isogenic rpoD+ and rpoD800 cells during steady-state growth and after temperature shift, in order to define the role of the sigma subunit in vivo. We have shown that sigma synthesis is regulated. After temperature shift-up, sigma behaves like other heat-shock proteins. The stimulation of sigma synthesis by heat shock is greater in mutant than in wild-type cells, possibly because the cell is responding to sigma limitation at high temperature by over-producing sigma. Mutant cells continue protein synthesis for a short time after shift-up and then shut off the synthesis of all proteins in response to the decreasing intracellular concentration of sigma. During the initial period of high protein synthesis, the relative expression of many proteins is changed in mutant cells. We argue that these changes are predominantly an indirect, rather than a direct effect of mutant sigma and are due to a change in the physiological state of mutant cells. Finally, we have shown that degradation of mutant sigma results in a decrease in synthesis of all major messenger RNA and stable RNA species. If other sigma factors are present in exponentially growing cells, they do not appear to be involved in a significant fraction of RNA synthesis.

Alleles↗
PubMed1983

Mutations in the Ion gene of E. coli K12 phenotypically suppress a mutation in the sigma subunit of RNA polymerase.

We have isolated spontaneous temperature-resistant revertants of a temperature-sensitive mutation (rpoD800) in the sigma subunit of E. coli K12 RNA polymerase. These revertants still contained the rpoD800 allele. They were mucoid, and sensitive to ultraviolet light and the radiomimetic agent nitrofurantoin, which are characteristics of lon mutants. One revertant, Tr29, was mapped to the lon region of the chromosome. Lon- rpoD800 double mutants were constructed, and were phenotypically indistinguishable from the spontaneous temperature-resistant revertant. It is the degradation-deficient property of lon mutants that is responsible for the suppression of the temperature-sensitive phenotype. We show that the rpoD800 sigma polypeptide is a substrate for the ion proteolytic system, and that mutations in lon decrease the rate of mutant sigma degradation. The rate of synthesis of mutant sigma was also affected in lon- strains. The net effect of lon-mutations was to increase the concentration of mutant sigma. We conclude that the temperature-sensitive phenotype results from insufficient concentration, rather than altered function, of the mutant protein.

Bacterial Proteins↗
PubMed1982

[Fosfomycin concentrations in serum and bile (author's transl)].

40 patients were given a single, short intravenous infusion of 4 g fosfomycin over a period of five to ten minutes. In 23 patients, the contents of the gall bladder were removed intra-operatively 30-105 minutes after the fosfomycin infusion. In 17 patients who had undergone cholecystectomy eight to ten days earlier, bile was obtained via a T-drain 30, 60, 120, 240 and 360 minutes after the fosfomycin infusion. Fosfomycin concentrations of 1-196 mg/l were present in the bile which had been removed intra-operatively. No correlation was found between the concentration and the time of removal. Patients with the highest alkaline phosphatase in serum, however, had the lowest fosfomycin concentrations. In the patients with T-drains, the highest concentrations (93 mg/l) were found 30 minutes after the fosfomycin infusion. By the sixth hour the concentrations had fallen to 19 mg/l.

Adult↗
PubMed1980

A new mutation rpoD800, affecting the sigma subunit of E. coli RNA polymerase is allelic to two other sigma mutants.

We have characterized a new mutation rpoD800 affecting the sigma gene of E. coli. Upon tranfer to high temperature, a strain with the rpoD800 mutation ceases growth within 30 min. We find that this mutation renders sigma about 10-fold more thermolabile than the wild type sigma at 45 degrees C in vitro. We have compared the temperature profile for inactivation of wild type and mutant sigma and find that the mutant inactivates at a temperature about 9 degrees C lower than does the wild type. The chromosomal locus affected by rpoD800 is shown to be allelic to the locus affected by the spontaneous mutants ts285 and alt-1. All three mutations result in altered sigma and in altered growth at high temperature. We argue that the single locus affected is the structural gene for the sigma subunit of E. coli RNA polymerase.

Alleles↗
PubMed1979

Altered chemical properties in three mutants of E. coli RNA polymerase sigma subunit.

We have analyzed some chemical properties of the sigma subunit of RNA polymerase from the sigma mutants: rpoD1 (Gross et al., 1978), rpoD2 (formerly known as alt-1) (Silverstone et al., 1972; Travers et al., 1978), and rpoD800 (Gross et al., 1979). Each of the three mutants is located at about 66 min on the E. coli genetic map and exhibits an alteration in the enzymatic properties of its sigma subunit. The tryptic peptides and isoelectric focusing behavior were analyzed for mutant and wild type sigma. A single, but different altered lysine tryptic peptide was observed for each mutant. No altered arginine tryptic peptides were observed. The rpoD800 mutant sigma showed an altered isoelectric point. These studies provide chemical evidence that the sigma polypeptide in all three mutants is altered and strongly support the conclusion that the mutations are in the structural gene for sigma.

Alleles↗