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R Zahn

Publications and source records attributed to R Zahn.

135 records · Page 8Linked to original sources
PubMed1988

Yeast mutants temperature-sensitive for growth after random mutagenesis of the chromosomal RAS2 gene and deletion of the RAS1 gene.

Saccharomyces cerevisiae strains with a disrupted RAS1 gene and with an intact RAS2 gene (ras1- RAS2 strains) grew well on both fermentable and nonfermentable carbon sources. By constructing isogenic mutants having a disrupted RAS1 locus and a randomly mutagenized chromosomal RAS2 gene, we obtained yeast strains with specific growth defects. The strain TS1 was unable to grow on nonfermentable carbon sources and galactose at 37 degrees C, while it could grow on glucose at the same temperature. The mutated RAS2 gene in TS1 cells encoded a protein with the glycines at positions 82 and 84 replaced by serine and arginine respectively. Both mutations were necessary for temperature sensitivity. We also isolated a mutant yeast that was unable to grow on nonfermentable carbon sources both at 30 and 37 degrees C, while growing on glucose at both temperatures. This phenotype was caused by a single chromosomal mutation, leading to the replacement of aspartic acid 40 of the RAS2 protein by asparagine. A ras1- yeast strain with a chromosomal RAS2 gene harbouring the three mutations together did not grow at any temperature using non-fermentable carbon sources, but it was able to grow on glucose at 30 degrees C, and not at 37 degrees C. The mutated proteins were much less effective than the wild-type RAS2 protein in the stimulation of adenylate cyclase, but were efficiently expressed in vivo. The possible roles of residues 40, 82 and 84 of the RAS2 protein in the regulation of adenylate cyclase are discussed.

Adenylyl Cyclases↗
PubMed1986

Suppression of defective RAS1 and RAS2 functions in yeast by an adenylate cyclase activated by a single amino acid change.

We have constructed the yeast strain TS1, with the RAS2 gene replaced by mutant allele encoding a partially defective gene product, and with an inactive RAS1 gene. TS1 cells accumulate as unbudded cells upon temperature shift from 30 to 37 degrees C, thus showing that the RAS1 and RAS2 gene functions are important for progression through the G1 phase of the cell cycle. After the isolation of revertants able to grow at the nonpermissive temperature, we have found that a chromosomal point mutation can bypass the G1 arrest of TS1 and cdc25 cells, and the lethality of ras1 ras2 mutants. The mutation predicts the replacement of threonine by isoleucine at position 1651 of yeast adenylate cyclase. The RAS-independent, as well as the RAS-dependent adenylate cyclase activity, is increased by the mutation. Like the wild-type enzyme, the RAS-dependent activity of the mutant adenylate cyclase is turned on by the GTP-bound form of the RAS2 protein. The amino acid sequence surrounding the threonine 1651 shows similarity with protein kinase substrates. Possible implications for the function of adenylate cyclase are discussed.

Adenylyl Cyclases↗
PubMed1986

Regeneration of the GTP-bound from the GDP-bound form of human and yeast ras proteins by nucleotide exchange. Stimulatory effect of organic and inorganic polyphosphates.

The regeneration of the GTP-bound from the GDP-bound form of purified human and yeast ras proteins occurs in vitro by a nucleotide-exchange reaction. For both human and yeast ras proteins the dissociation of the protein-bound GDP is the rate-limiting step in the presence of Mg ions. The rate of formation of the ras X GTP complex is stimulated by weak Mg2+-chelating agents like ATP and inorganic polyphosphates and, to a lesser extent, by ADP. This suggests a possible mechanism of regulation of ras-dependent pathway(s) by intracellular metabolic products.

Adenosine Triphosphate↗
PubMed1986

[Thrombolytic therapy and balloon dilatation. The effect on infarct time, reperfusion and reocclusion].

127 patients, admitted within six hours of onset of symptoms of acute transmural myocardial infarction, received at first 250 000 U streptokinase intravenously over 20 min, followed by an intracoronary infusion of 250 000 U after coronary angiographic demonstration of the infarct vessel. Those in whom the infarct vessel was closed were randomized into two groups. An attempt at recanalization was made either by thrombolysis alone, through a specially developed 3F catheter (group I, 64 patients), or by thrombolysis and dilatation with 4F Grüntzig balloon catheter (group II, 63 patients). There was no significant difference between the two groups with regard to sex, age, infarct site, creatine-kinase level and interval between onset of symptoms and treatment. Re-perfusion rate for group I was 92% (59 patients), for group II 89% (56 patients). Re-occlusion during the hospital stay occurred in 10 of 59 patients in group I, in 9 of 55 in group II. Re-occlusion occurred in only 8% (3 patients) after successful dilatation, but in 35% (6 patients) after failed dilatation. In the subsequent six months further occlusions were observed in seven group I and two group II patients. Combined drug-mechanical recanalization thus increased the re-perfusion rate, shortened the infarction time and made possible full revascularization by subsequent dilatation which led to a reduction in the re-occlusion rate.

Aged↗
PubMed1986

[Combined use of thrombolysis and PTCA in myocardial infarct. Effect on global and regional ventricular function].

The study was performed to evaluate the combined effect of thrombolysis therapy and percutaneous coronary transluminal angioplasty (PTCA) on global and regional left ventricular function. In 127 patients with acute transmural myocardial infarction combined intravenous (250 000 U) and intracoronary (50 000 U) streptokinase therapy was started. When the infarct related vessel was occluded mechanical recanalization was performed with recanalization by Gruentzig balloon catheters. Patients were randomized in two groups, group I, n = 64, thrombolysis without PTCA; group II, n = 63, thrombolysis with PTCA. Both groups demonstrated no difference in relation to sex, age, infarct location, as well as CPK levels and time between onset of symptoms and start of treatment. First coronary angiography showed an open vessel in 23/64 patients (36%) of group I and in 12/63 patients (19%) of group II (p less than 0.001). Mechanical recanalization with 3 F catheters could be achieved in 27/41 patients (66%) of group I and with 4 F catheters in 26/51 patients (51%) of group II. In 9/41 patients (22%) of group I and in 18/51 patients (35%) in group II reperfusion took place before mechanical recanalization could be performed or occurred during superselective thrombolysis therapy, when mechanical recanalization failed. Thus, reperfusion rate in group I was 59/64 patients (92%) and in group II 56/63 patients (89%). PTCA was attempted in 55/56 patients in group II with a success rate of 65% and reocclusion rate of 4%. During hospital stay, reocclusion occurred in 10/59 patients in group I (17%) and in group II in 9/55 patients (16%). The patients were divided in those with and without successful angioplasty. Reocclusion was found in 3/36 patients (8%) and 6/17 patients (35%), respectively. Improvement with PTCA of regional and global left ventricular function was observed in patients with anterior myocardial infarction. With combined medical-mechanical recanalization, reperfusion rate can be increased and infarct time shortened, thus, providing the possibility of full revascularization by PTCA, improving coronary blood flow as well as improving global and regional left ventricular function.

Angioplasty, Balloon↗
PubMedDate not supplied

Transmission electron microscopy of GroEL, GroES, and the symmetrical GroEL/ES complex.

Two new 2-D crystal forms of the Escherichia coli chaperone GroEL (cpn60) 2 x 7-mer have been produced using the negative staining-carbon film (NS-CF) technique. These 2-D crystals, which contain the cylindrical GroEL in side-on and end-on orientations, both possess p21 symmetry, with two molecules in the respective unit cells. The crystallographically averaged images correlate well with those obtained by other authors from single particle analysis of GroEL and our own previous crystallographic analysis. 2-D crystallization of the smaller chaperone GroES (cpn10) 7-mer has also been achieved using the NS-CF technique. Crystallographically averaged images of GroES single particle images indicate considerable variation in molecular shape, which is most likely due to varying molecular orientation on the carbon support film. The quaternary structure of GroES does, nevertheless, approximate to a ring-like shape. The complex formed by GroEL and GroES in the presence of ATP at room temperature has been shown to possess a symmetrical hollow ellipsoidal conformation. This symmetrical complex forms in the presence of a 2:1 or greater molar ratio of GroES:GroEL. At lower molar ratios linear chains of GroEL form, apparently linked by GroES in a 1:1 manner, which provide supportive evidence for the ability of both ends of the GroEL cylinder to interact with GroES. The apparent discrepancy between our data and that of other groups who have described an asymmetrical "bullet-shaped" (holo-chaperone) GroEL/ES complex is discussed in detail.

Chaperonin 10↗