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Biomedical subjects

S Hahn

Publications and source records attributed to S Hahn.

At least 199 records · Page 11Linked to original sources
PubMed1991

The yeast general transcription factor TFIIA is composed of two polypeptide subunits.

The general transcription factor TFIIA was purified from yeast. A key step in the purification was affinity chromatography using a column containing the adenovirus major late promoter with bound recombinant TFIID to which TFIIA binds with high affinity. TFIIA activity copurifies with two polypeptides of molecular mass 32 and 13.5 kDa. Elution and renaturation of these two polypeptides from sodium dodecyl sulfate-polyacrylamide gels showed that both polypeptides were required for TFIIA activity. TFIIA activity was measured by both a native gel shift assay and by in vitro complementation of transcription using yeast nuclear extracts depleted of TFIIA. The purified renatured yeast TFIIA also complements basal level transcription using a mammalian transcription system depleted of TFIIA. Native TFIIA has an apparent molecular mass of approximately 90 kDa measured by gel filtration chromatography. TFIIA binds to a TFIID.TATA element.DNA complex with an apparent equilibrium dissociation constant (KD) of 20 pM. This affinity is about 100-fold greater than the affinity of TFIID for TATA elements and much greater than the affinity of TFIIA for TFIID not bound to DNA.

Cell Nucleus↗
PubMed1991

Dominant negative mutations in yeast TFIID define a bipartite DNA-binding region.

Genetic analysis showed that the conserved C-terminal 180 amino acids of yeast TFIID contain all the essential functions for growth of yeast and response to acidic transcriptional activation signals. A genetic screen was used to identify functionally important residues within this C-terminal region. Five dominant TFIID mutations were isolated that had lost the ability to bind DNA. Four of these mutations were single amino acid substitutions in the most N-terminal of two 66-67 amino acid repeats in TFIID. Analogous mutations made in the most C-terminal repeat all failed to bind DNA and inhibited growth of cells, suggesting that the DNA-binding function of TFIID is partitioned between the two repeated regions. Overproduction of wild-type TFIID rescued the dominance of the TFIID mutants, suggesting that the mutant proteins are dominant because they compete with wild-type TFIID for binding to one or more essential transcription factors.

Amino Acid Sequence↗
PubMed1991

Metabolism of unusual membrane phospholipids in the marine sponge Microciona prolifera.

Sponges are unique in regard to membrane phospholipid composition. Features virtually without parallel in other organisms are the predominance of the C26-C30 polyenoic acids (demospongic acids) in the phosphatidylethanolamines (PE) and the attachment of identical acyl groups to the glycerol moiety. The biosynthesis and disposition of these unusual phospholipids were followed in the marine sponge Microciona prolifera where PE ( delta 5,9-26:2, delta 5,9-26:2) is a major molecular species. Incorporation experiments with radiolabeled fatty acids, bases, and intact phospholipids revealed the de novo biosynthesis of the two major phosphatides, phosphatidylethanolamines (PE) and phosphatidylcholines (PC), via the cytidine pathway as in higher animals, with ethanolamine selectively incorporated into PE( delta 5,9-26:2, delta 5,9-26:2). Methylation of PE and random acyl chain migration across different phospholipid classes were marginal, but the exchange of PC for PE, apparently mediated by the action of phospholipase, was indicated after uptake of the unnatural PC( delta 9-27:1, delta 9-26:1). The present study demonstrates in the most primitive multicellular animals a phospholipid metabolic pattern similar to that in higher organisms, with unique acyl and phosphoethanolamine transferases apparently involved in the biosynthesis of the (demospongic) di-C26-acyl-PE molecular species.

Animals↗
PubMed1991

[Not Available].

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Education, Medical↗
PubMed1991

Ras oncogenes amplify lymphokine (interleukin 3, granulocyte-macrophage colony-stimulating factor) induction by calcium ionophore.

Interleukin 3 (IL-3) expression in PB-3c mastocytes is transiently induced in vitro by treatment with the drug A23187, a calcium ionophore, or constitutively following ras-dependent transformation in vivo. While the mechanism of oncogenically induced IL-3 expression is not clear, A23187-mediated lymphokine mRNA accumulation is primarily the result of calcium-dependent mRNA stabilization. We investigated whether the expression of various ras alleles influenced IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA induction by A23187. It was found that activated forms of ras potentiated ionophore-mediated lymphokine mRNA accumulation. This enhancement involves a post-transcriptional mechanism, as ionophore-induced lymphokine mRNAs are significantly more stable in ras oncogene-expressing lines than in the control line. We propose that one way by which ras genes exert their oncogenic potential is by extending the half-life of short-lived growth factor mRNAs.

Blotting, Northern↗
PubMed1991

[Contribution of pathologic anatomy and forensic medicine to a theory of suicide in Germany from 1870 to 1933].

Alarming suicide records encouraged the community of science-oriented medicine in the last third of the 19th century to pay more attention to the suicide phenomenon and, in the context of pathological anatomy, to try to identify causes as well as possible approaches to prophylaxis and therapy. Hopes were not satisfied for specific morphological findings from suicide cases, as may be seen from various research results reported in this paper. Nevertheless, this approach had to it social potentials helpful in reducing bias and sanctions against suicides. However, attempts failed to enlarge scientific and social effectiveness by closer coordination of scientific research with efforts to control suicide at psychic and social levels and in public life. Science-oriented medicine actually retreated to biological factors, even before the first world war, and thus left the people concerned exposed to social degradation and marginalisation, as suicide continued to be considered an inescapable fate.

Forensic Medicine↗
PubMed1990

[Hyaluronidase release in bull sperm--influence of media and temperature].

Studies were conducted into behaviours of total and extracellular hyaluronidase activities of bull semen under selected incubation phenomena. Particular attention was given to effects generated by media of high and physiological ion strengths (385 mosm and 305 mosm), in vitro capacitation treatment, and effects of various washing techniques as well as incubation temperatures. Total hyaluronidase activity was clearly lowered in washed ejaculate sperms, as compared to original sperm, with extracellular enzyme activity, however, being unchanged. Hyaluronidase activity was also lower in deep-frozen sperm. Increase in extracellular and total hyaluronidase activity was at its highest under the impact of cattle serum albumin and with a defined temperature-time regime (four hours of comparative incubation in a medium of physiological ion strength at 35 degrees C, 37 degrees C, 39 degrees C, 41 degrees C, and 45 degrees C). Release of hyaluronidase was most clearly inducible after pretreatment in medium of physiological ion strength and by four hours of incubation at 39 degrees C. The preliminary conclusion is that the values so far recorded appeared to reflect some superimposition of physiological and degenerative processes which could not be distinguished from each other under the experimental conditions chosen for the studies.

Animals↗
PubMed1989

Unusual pattern of fatty acid biosynthesis. Evidence for C-19 desaturase activity in freshwater sponges.

The two long chain fatty acids common in marine demosponges, (5Z, 9Z)-5,9-hexacosadienoic (delta 5,9-26:2) and (5Z, 9Z, 19Z)-5,9,19-hexacosatrienoic (delta 5,9,19-26:3) acids), were identified also as the major phospholipid components in the freshwater sponge Ephydatia fluviatilis. Whereas the typical marine sponge Microciona prolifera biosynthesizes the delta 5,9,19-26:3 acid solely by homologation of exogenous palmitoleic acid (delta 9-16:1) and subsequent desaturation at positions 5 and 9, it was found that the freshwater sponge could further desaturate the delta 5,9-26:2 acid to the triene, indicating for the first time the existence of delta 19 -desaturase activity in a living organism.

Animals↗
PubMed1989

[The internist and general practitioner in ambulatory care--similarities and limits].

As a contribution to a self-appreciation of internal medicine which must newly be thought through under the modern conditions of medicine and society is tried to determine limits and communities of this specialty in the ambulatory basic medical care with regard to the general medicine orientating to the activities as a family doctor.

Ambulatory Care↗
PubMed1989

Isolation of the gene encoding the yeast TATA binding protein TFIID: a gene identical to the SPT15 suppressor of Ty element insertions.

We report the cloning of the gene that encodes the yeast TATA binding protein TFIID. TFIID contains 240 amino acids and has no obvious sequence similarity to other known proteins. TFIID was synthesized in vitro and in two separate assays behaved identically to the protein purified from yeast. TFIID bound to TATA elements from the adenovirus major late promoter (TATAAAA) and the yeast LEU2 promoter (TATTTAA) and formed protein-DNA complexes stable to electrophoresis only in the presence of TFIIA. In vitro-synthesized yeast TFIID also complemented a mammalian in vitro transcription system that lacked TFIID. Comparison of the yeast TFIID gene with the yeast SPT15 gene (suppressor of Ty element insertions) showed that the two genes are identical. This finding indicates that the yeast TFIID activity defined in vitro is responsible for specific transcription in vivo.

Amino Acid Sequence↗
PubMed1989

[Antisemitism in science and the health politics of the Weimar Republic--with special remembrance of Julius Moses (1868-1942)].

Fifty years after the Jew-baitings in Fascist Germany the phenomenon of race-hatred and race-separation remains politically actual up to now and commits ourselves to remembrance, meditation and active attitude aginst all its forms. The events after 1933 appear as an appalling escalation of antisemitism which was practised already in the period of the Weimar Republic. A particular appreciation of all those persons who recognized this danger at the right time, came up against it and finally became victims is left to us. Thereby the humanistic activities of Julius Moses (1868-1942) are made mention of.

Germany↗
PubMed1989

Five intermediate complexes in transcription initiation by RNA polymerase II.

A native gel electrophoresis DNA binding assay was used to resolve complexes formed on the adenovirus Major Late Promoter by general transcription factors and RNA polymerase II. Five sets of complexes containing distinct components were identified. These complexes were generated by sequential binding of TFIID, TFIIA, TFIIB, RNA polymerase II, and TFIIE. The relative positions of each of the factors in the complexes were determined by DNAase I footprint analysis. TFIIA, derived from yeast or mammalian cells, formed a complex with yeast TFIID and the TATA element. TFIIB bound to this complex and probably acts as a "bridge" to the polymerase and the initiation site. The addition of ATP or dATP, necessary for "activation" of transcription, resulted in an alteration of the footprint in the +20 to +30 region, the same area protected upon addition of TFIIE to the initiation complex. Addition of ribonucleotide triphosphates generated new complexes that contained accurately initiated transcripts associated with the transcription machinery and the template DNA. A model for the interactions of components in initiation of transcription by RNA polymerase II is proposed.

Adenoviridae↗
PubMed1989

Identification of a yeast protein homologous in function to the mammalian general transcription factor, TFIIA.

The yeast homolog of the mammalian RNA polymerase II general transcription factor TFIIA has been identified by complementation of a mammalian in vitro transcription system depleted for TFIIA. Like the mammalian factor, the yeast protein does not bind DNA, alters the size of the TFIID DNase I footprint at the adenovirus major late promoter, and forms specific TFIIA-TFIID-DNA complexes which are stable during electrophoresis in native acrylamide gels. The partially purified yeast factor was used to investigate its effect on the binding of TFIID to the major late promoter. Contrary to earlier models, we find that TFIIA does not significantly change the affinity or kinetics of TFIID binding, suggesting that it acts by altering the conformation of TFIID and/or by serving as a bridge between TFIID and the other general transcription factors.

Adenoviridae↗