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Biomedical subjects

A Kuhn

Publications and source records attributed to A Kuhn.

At least 163 records · Page 9Linked to original sources
PubMed1987

[Benign and malignant granular cell tumors. An immunohistochemical classification of tumor cells].

Eight benign and three malignant granular cell tumors were characterized by means of antibodies and antisera against keratin, desmin, epithelial membrane antigen, factor VIII-related protein, lysozyme, myelin basic protein, myoglobin, neurone-specific enolase, S 100 protein, myelin-associated protein (Leu 7), glial fibrillary acidic protein, vimentin, and neurofilament. All benign granular cell tumours showed positive staining of the tumor cells to antibodies against vimentin, S 100 protein, and neurone-specific enolase; myelin-associated protein (Leu 7), in contrast, was only detectable in a few tumor sections. Histogenetically the granular cells may be classified as Schwann's cells which lost their expression of laminin. The three malignant granular cell tumors showed a staining pattern significantly different from that of the benign tumours. Thus, only neurone-specific enolase was detectable in all the tumors, whereas S 100 protein and vimentin could not be demonstrated but in one and two, resp., out of three tumors.

Antibodies, Monoclonal↗
PubMed1987

A novel promoter in the mouse rDNA spacer is active in vivo and in vitro.

We have identified a novel RNA polymerase I (pol I) transcription initiation site within the 'non-transcribed' spacer of mouse rDNA. This spacer promoter is located about 2 kb upstream of the 45S pre-rRNA promoter and directs specific transcription initiations both in a cell-free system using truncated templates and in vivo after transfection into mouse cells. The spacer promoter contains an 11 out of 16 bases match to the core element of the major ribosomal gene promoter and is oriented in the same direction. It exerts a significantly lower transcriptional activity as compared to the 45S pre-rRNA promoter. The elongation of transcripts initiated at the spacer promoter is stopped at a termination signal located 170 bp upstream of the pre-rRNA start site. Since it has been previously shown that, in addition to its terminator function, the same sequence motif acts as an upstream element of the adjacent gene promoter, the function of the spacer promoter may be to capture free pol I molecules and drive them to the gene promoter in order to achieve the high level of transcription characteristic of eukaryotic rRNA genes.

Animals↗
PubMed1987

Recombinant forms of M13 procoat with an OmpA leader sequence or a large carboxy-terminal extension retain their independence of secY function.

The assembly of phage M13 procoat protein into the plasma membrane of Escherichia coli is independent of the secY protein. To test whether this is caused by the unusually small size of procoat, we fused DNA encoding 103 amino acids to the carboxy-terminal end of the procoat gene. The resulting fusion protein, which attains the same membrane-spanning conformation as mature coat protein, still does not require the secY function for membrane assembly. To determine whether the leader sequence governs interaction with the secY protein, we genetically exchanged the leader peptides between procoat and pro-OmpA, a protein which does require secY for its membrane assembly. Each of the resulting hybrid proteins assembles across the plasma membrane, though at a reduced rate. Membrane assembly of the fusion of procoat leader and OmpA required secY function, whereas assembly of the pro-OmpA leader/coat protein fusion was independent of secY. Properties of the entire procoat molecule, rather than its small size or a specific property of its leader peptide determines its mode of membrane assembly.

Bacterial Outer Membrane Proteins↗
PubMed1987

Prohead core of bacteriophage T4 can act as an intermediate in the T4 head assembly pathway.

Bacteriophage T4 assembly was impaired in Escherichia coli hdB3-1 at an incubation temperature below 30 degrees C. Naked prohead cores (head scaffold) bound to the inner surface of the plasma membrane accumulated, and the major shell protein (gp23) precipitated into visible intracellular aggregates in the cytoplasm. Shifting the temperature to 42 degrees C allowed newly synthesized gp23 to assemble around the accumulated cores. We conclude that synchronous assembly of the scaffold and shell is not obligatory and that naked cores can serve as intermediates in the T4 assembly pathway.

Cell Membrane↗
PubMed1987

[Immunohistologic differential diagnosis of skin tumors in routinely embedded paraffin sections].

Thirty-nine skin tumors of epithelial, mesenchymal, and neuroectodermal origin were studied using antibodies against intermediate filaments and other cell proteins. Formol-fixed and paraffin-embedded material was reconstituted and stained with antibodies against epithelial cells (keratin, epithelial membrane antigen, carcinoembryonic antigen), mesenchymal and histiocytic cells (vimentin, alpha-1-antichymotrypsin, alpha-1-antitrypsin, lysozyme), nerve tissue (neurofilament, glial fibrillary acidic protein, myelin basic protein, myelin-associated protein, neuron-specific enolase), vessels (factor-VIII-related protein), basal cell lamina (laminin) and S-100 protein. Tumor cells displayed the same antibody pattern found in the normal cell type. It is recommended that immunotyping be started with three antibodies to allow gross classification into epithelial (keratin positive), mesenchymal (vimentin positive) and neuroectodermal (vimentin and S-100 protein positive) tumors; then, in a second step, the tumors can be subclassified by the other more specific antibodies listed above. All antibodies used in this study are commercially available and provide reliable results.

Antigens, Neoplasm↗
PubMed1986

A transcription terminator located upstream of the mouse rDNA initiation site affects rRNA synthesis.

Mouse ribosomal genes have a short sequence upstream of the transcription initiation site that is related in structure and function to the terminator boxes previously identified at the 3' end of the transcription unit. This upstream terminator recognizes the same protein factor as the 3'-terminal sites and is able to terminate RNA polymerase I transcription in vitro. S1 mapping and nucleolar run-on experiments reveal the presence of 5'-terminal spacer transcripts that are terminated at this site. These transcripts probably derive from spacer promoters, one of which has been identified approximately 2 kb upstream of the pre-rRNA start site. The interaction of a specific nuclear factor with the upstream terminator increases the efficiency of initiation, suggesting that transcription termination and initiation at the adjacent promoter work in an interrelated fashion.

Animals↗
PubMed1986

Both hydrophobic domains of M13 procoat are required to initiate membrane insertion.

M13 procoat protein has two hydrophobic domains, one in the leader peptide and one which anchors the mature coat protein in the membrane. Disruption of the membrane anchor region by insertion of arginyl residues does not yield periplasmic coat protein. Instead, the rate of membrane assembly is slowed greater than 100-fold (t1/2 less than 5 s for wild-type, t1/2 greater than 10 min for mutant). The hydrophobic region of mature coat protein not only functions as a membrane anchor, but has an important role in the membrane assembly process per se.

Amino Acid Sequence↗
PubMed1986

[Immunohistochemical studies of paraffin-embedded material of solitary cutaneous neurofibromas].

Nine cutaneous solitary neurofibromas have been studied using antibodies against vimentin, S 100 protein, lysozyme, myoglobin, factor VIII, neurofilament, neuron specific enolase, and myelin-associated antigen. Most of the tumor cells showed positive reactions to S 100 protein and vimentin with different patterns of staining. Whereas vimentin was detected in the cell periphery, S 100 protein was concentrated in the perinuclear area and distinct in the cytoplasm. About 60 percent of the tumor cells revealed positive staining for laminin. Myoglobin, neurofilament, and neuron specific enolase could not be proved in the tumor tissue. Our results suggest that the majority of neurofibroma cells may derive from Schwann's cells.

Humans↗
PubMed1986

[Squamous epithelial cancer in lichen ruber hypertrophicus--a case report with a review of the literature].

Spinocellular carcinoma developed in a 19-year-old lesion of lichen ruber hypertrophicus of the lower leg. In the literature,24 cases of spinocellular carcinoma in lesions of cutaneous lichen ruber have been reported. X-ray and arsenic treatment has often preceded malignant transformation. Another risk factor seems to be the chronic hypertrophic type of lichen ruber located on the lower extremities.

Adult↗
PubMed1986

Genetic variation of an acid phosphatase (Acp-2) in the laboratory rat: possible homology with mouse AP-1 and human ACP2.

A genetic locus controlling the electrophoretic mobility of an acid phosphatase in the rat (Rattus norvegicus) is described. The locus, designed Acp-2, is not expressed in erythrocytes but is expressed in all other tissues studied. The product of Acp-2 hydrolyzes a wide variety of phosphate monoesters and is inhibited by L(+)-tartaric acid. Inbred rat strains have fixed either allele Acp-2a or allele Acp-2b. Codominant expression is observed in the respective F1 hybrids. Backcross progenies revealed the expected 1:1 segregation ratio. Possible loose linkage was found between the Acp-2 and the Pep-3 gene loci at a recombination frequency of 0.36 +/- 0.06.

Acid Phosphatase↗
PubMed1986

Nutritional Factors Affecting the Ratio of Solvents Produced by Clostridium acetobutylicum.

Fermentation of whey by Clostridium acetobutylicum yielded butanol and acetone in a ratio of approximately 100:1. This ratio amounted to only 2:1 in synthetic media with glucose, lactose, or glucose plus galactose as substrates. Removal of citrate from whey and addition of minerals resulted in an increase in the amount of acetone produced. Experiments carried out in a chemostat with a low-phosphate synthetic medium revealed that the butanol/acetone ratio could be increased from 2:1 to 3.8:1 by cofermentation of l-lactate and from 2:1 to 8:1 by iron limitation. The performance of the fermentation in a low-iron glucose medium above pH 5.1 yielded l-lactate as the main product.

Journal Article↗
PubMed1985

Conserved residues of the leader peptide are essential for cleavage by leader peptidase.

Gene 8 of bacteriophage M13 codes for procoat, the precursor of its major coat protein. Gene 8 has been cloned into a plasmid and mutagenized. We have isolated mutants of this gene in which procoat is synthesized but is not processed to coat protein. We now describe mutants in the leader region of procoat, at positions -6, -3, and -1 with respect to the leader peptidase cleavage site. These positions are quite conserved among the leader peptides of various pre-proteins. Each of these mutant procoats is synthesized at a normal rate and inserts correctly into the plasma membrane, as judged by its accessibility to protease in intact spheroplasts. Procoat accumulates, largely in its transmembrane form, and is not cleaved to coat. In detergent extracts, the mutant procoats are very poor substrates for added leader peptidase. We conclude that these 3 residues are not conserved for insertion across the membrane but are part of an essential recognition site for the leader peptidase.

Bacteriophages↗
PubMed1985

Isolation of mutants in M13 coat protein that affect its synthesis, processing, and assembly into phage.

The major coat protein (gene 8 protein) of bacteriophage M13 has been studied intensively as a model of membrane assembly, protein packing, and protein-DNA interactions. Because this protein is essential for assembly of the phage, very few mutants have been isolated. We have therefore cloned the gene 8 into a plasmid under control of the araB promoter. In the presence of arabinose, the cloned gene is expressed at a rate comparable to that in an M13-infected cell. Plasmid-derived procoat is inserted across the plasma membrane and processed to coat at a normal rate. The coat can support plaque formation by a defective M13 virus (M13am8) with an amber mutation in its procoat gene. This complementation assay was used to screen the mutagenized, cloned gene 8 for mutants which fail to make fully functional coat. Mutants were obtained which fail to synthesize procoat, which do not convert procoat to mature coat protein, or in which the coat protein is incapable of assembling into infectious virions.

Arabinose↗
PubMed1985

Manipulation of intracellular magnesium content in polymyxin B nonapeptide-sensitized Escherichia coli by ionophore A23187.

Escherichia coli B cells were sensitized to ionophore A23187 by polymyxin B nonapeptide, and the induced magnesium and potassium ion fluxes were studied. Combined ionophore treatment permeabilized the cytoplasmic membrane of E. coli in an ion-specific manner and allowed the manipulation of intracellular Mg2+ content from the outside. A23187-induced Mg2+ efflux or influx was dependent on the free Mg2+ concentration gradient between the outside and inside of the cytoplasmic membrane and on the pH gradient. Most of the intracellular Mg2+ was bound, whereas only 1 to 2 mM was free in solution in the cellular sap.

Biological Transport↗
PubMed1985

Productive phage infection in Escherichia coli with reduced internal levels of the major cations.

Bacteriophage-induced changes in the intracellular levels of the major cations of Escherichia coli were studied to investigate the role of ion concentrations for bacteriophage assembly in vivo. Infection of E. coli by phage T4, P1, or lambda caused a transient reduction of intracellular levels of potassium, magnesium, and polyamines. Phages T3 and T7, however, had no detectable effect on the cation concentrations within the cell. In all cases, any reduction in the ion concentrations was restored later in infection. When the intracellular potassium concentration was lowered from 325 to 150 mM with a different osmotic growth medium, the number of phage progeny was only slightly reduced (by a factor of two). On additional reduction of the intracellular magnesium concentration from 100 to 50 mM by adding the antibiotic polymyxin B to the infected cells, T4 infections, but not T3 or T7, were markedly affected. These studies show that T3, T4, and T7 phage assembly can efficiently occur in vivo over a broad spectrum of ion concentrations.

Bacteriophage lambda↗