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Biomedical subjects

B Müller

Publications and source records attributed to B Müller.

At least 343 records · Page 19Linked to original sources
PubMed1990

T7 endonuclease I resolves Holliday junctions formed in vitro by RecA protein.

T7 endonuclease I is known to bind and cleave four-way junctions in DNA. Since these junctions serve as analogues of Holliday junctions that arise during genetic recombination, we have investigated the action of T7 endonuclease I on recombination intermediates containing Holliday junctions. We find that addition of T7 endonuclease I to strand exchange reactions catalysed by RecA protein of Escherichia coli leads to the formation of duplex products that correspond to 'patch' and 'splice' type recombinants. Resolution of the recombination intermediates occurs by the introduction of nicks at the site of the Holliday junction. The recombinant molecules contain 5'-phosphate and 3'-hydroxyl termini which may be ligated to restore the integrity of the DNA.

DNA, Bacterial↗
PubMed1990

Gene expression during tuber development in potato plants.

Potato tubers are modified stems that have differentiated into storage organs. Factors such as day-length, nitrogen supply, and levels of the phytohormones cytokinin and gibberellic acid, are known to control tuberization. Morphological changes during tuber initiation are accompanied by the accumulation of a characteristic set of proteins, thought to be involved in N-storage (i.e. patatin) or defense against microbial or insect attack (i.e. proteinase inhibitor II). Additionally, deposition of large amounts of starch occurs during tuber formation, which is paralleled by an increase in sucrose synthase and other enzymes involved in starch biosynthesis (i.e. ADP-glucose pyrophosphorylase, starch synthases, and branching enzyme). Potential controlling mechanisms for genes expressed during tuberization are discussed.

Carboxylic Ester Hydrolases↗
PubMed1990

Dimerization of human immunodeficiency virus type 1 reverse transcriptase. A target for chemotherapeutic intervention.

Recombinant human immunodeficiency virus type 1 reverse transcriptase has been used to investigate the process of dimer formation and the properties of the different mono- and dimeric forms of the enzyme. The studies show that reverse transcriptase activity is exclusively confined to the dimeric forms. As we also demonstrate, the association rate constant between the monomers is relatively low so that the dimer-monomer equilibrium is very slowly established. This offers a new and potentially interesting target for antiviral chemotherapy with presumably higher specificity than the currently used nucleoside analogs (Yarchoan, R., Mitsuya, H., Myers, C.E., and Broder, S. (1989) N. Eng. J. Med. 321, 726-738), which in their active triphosphorylated form are also inhibitors of cellular polymerases.

Acquired Immunodeficiency Syndrome↗
PubMed1990

[Ulcer symptoms without demonstration of ulcer: causative therapy with demonstration of Helicobacter pylori].

Helicobacter pylori-associated gastritis was found by endoscopy in 15 (= 28%) out of 53 patients presenting gastric pain of ulcer type without macroscopically detectable lesion of the gastric mucosa. Following a treatment of four weeks with bismuth subcitrate tablets (2 x 2 tablets daily), in 73% improvement of histological findings and in 87% elimination of bacteria could be attained. Thus, this causal therapy had a favourable effect on patient complaints.

Adult↗
PubMed1990

Characterization of the DNA binding activity of stable RecA-DNA complexes. Interaction between the two DNA binding sites within RecA helical filaments.

The DNA-binding, annealing and recombinational activities of purified RecA-DNA complexes stabilized by ATP gamma S (a slowly hydrolysable analog of ATP) are described. Electrophoretic analysis, DNase protection experiments and observations by electron microscopy suggest that saturated RecA complexes formed with single- or double-stranded DNA are able to accommodate an additional single strand of DNA with a stoichiometry of about one nucleotide of added single-stranded DNA per nucleotide or base-pair, respectively, of DNA resident in the complex. This strand uptake is independent of complementarity or homology between the added and resident DNA molecules. In the complex, the incoming and resident single-stranded DNA molecules are in close proximity as the two strands can anneal in case of their complementarity. Stable RecA complexes formed with single-stranded DNA bind double-stranded DNA efficiently when the added DNA is homologous to the complexed strand and then initiate a strand exchange reaction between the partner DNA molecules. Electron microscopy of the RecA-single-stranded DNA complexes associated with homologous double-stranded DNA suggests that a portion of duplex DNA is taken into the complex and placed in register with the resident single strand. Our experiments indicate that both DNA binding sites within RecA helical filaments can be occupied by either single- or double-stranded DNA. Presumably, the same first DNA binding site is used by RecA during its polymerization on single- or double-stranded DNA and the second DNA binding site becomes available for subsequent interaction of the protein-saturated complexes with naked DNA. The way by which additional DNA is taken into RecA-DNA complexes shows co-operative character and this helps to explain how topological problems are avoided during RecA-mediated homologous recombination.

Adenosine Triphosphate↗
PubMed1990

Enzymatic formation and resolution of Holliday junctions in vitro.

E. coli RecA protein promotes homologous pairing and reciprocal strand exchange reactions between duplex DNA molecules in vitro. Reaction intermediates contain Holliday junctions that are driven along the DNA at a maximal rate approaching 1000 bases per minute. T4 endonuclease VII cleaves Holliday junctions in vitro, and its inclusion in RecA-mediated reactions leads to the rapid formation of heteroduplex products. Product analysis indicates patch and splice recombinant molecules similar to those expected from in vivo recombination events. The combined formation and resolution of Holliday junctions has led us to propose a model for resolution based on the structure of RecA-DNA helices. One feature of this model is that resolution, which gives rise to the two types of recombinant product, may occur without need for isomerization of the junction.

Bacteriophage phi X 174↗
PubMed1990

A physical map and analysis of the murine C kappa-RS region show the presence of a conserved element.

Lambda-producing B lymphocytes have frequently deleted one or, more often, both Ig kappa loci. This deletion is mediated by the rearrangement of an element which lies 3' of C kappa and which is called RS (recombining sequence) in the mouse and Kde (kappa-deleting element) in the human. The tight correlation between V lambda to J lambda rearrangements and an RS-mediated deletion may indicate that sequences in the C kappa-RS region are controlling the activation of the Ig lambda locus. We have linked the C kappa exon and the RS element by phage cloning and compared the C kappa-RS region to the previously cloned human C kappa-Kde region. The distance between C kappa and RS is 25 kb and is thus similar to the distance of 24 kb separating the human C kappa exon and Kde element. Both mouse and man carry a conserved sequence of 470 bp (Rx) which lies 9 kb 3' of the mouse C kappa and 12 kb 3' of the human C kappa exon. The conserved mouse Rx sequence contains part of the kappa 3' enhancer.

Animals↗
PubMed1990

Genetic evidence from 7 families that the apolipoprotein B gene is not involved in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is the most common genetic form of hyperlipidemia in which affected individuals manifest multiple lipoprotein phenotypes. Although the molecular defect is still unknown, several kinetic studies have demonstrated increased turnover rates of apolipoprotein B (apo B) in patients with FCHL, irrespective of their lipoprotein phenotype. Using 3 restriction fragment length polymorphisms (RFLPs) of the apo B gene (XbaI, MspI and EcoRI) we have investigated 33 families which fulfill the diagnostic criteria of FCHL. No significant difference in allele frequency was found between 33 unrelated individuals with FCHL and 107 normolipidemic controls. 3-RFLP haplotypes were constructed in each pedigree. A co-segregation analysis was performed in 7 informative families. In no family was co-segregation observed between the haplotype of the apo B gene and the phenotype of FCHL. These data are not compatible with the hypothesis that FCHL is caused by mutations of the apo B gene acting as a simple mendelian trait.

Adult↗
PubMed1990

Biochemical characterization of a putative axonal guidance molecule of the chick visual system.

Temporal retinal axons growing in vitro on carpets of tectal membranes are deflected by cell membranes of posterior tectum. The activity responsible for this deflection can be abolished by antibodies raised against tectal membranes and the corresponding Fab fragments. Analysis of tectal membranes by two-dimensional gel electrophoresis and immunoblotting reveals a 33 kd glycoprotein that has a higher concentration in posterior than in anterior tectum. Its expression is developmentally regulated, and it is sensitive to phosphatidylinositol-specific phospholipase C. These are properties expected for a molecule responsible for the phenomena observed in experiments on in vitro guidance of retinal axons.

Animals↗
PubMed1990

Axonal guidance in the chick visual system: posterior tectal membranes induce collapse of growth cones from the temporal retina.

Membranes from posterior and anterior thirds of the chick optic tectum were added to explants from nasal and temporal retina. Posterior membranes, and to a lesser extent anterior membranes, cause temporal growth cones to collapse and their axonal processes to retract. Neither tectal source has an effect on nasal growth cones. We interpret these results to mean that there is a tectal activity, stronger in the posterior than the anterior region of the tectum, which helps guide growth cones during the development of the retinotectal map. We believe that in vivo this activity helps to steer temporal growth cones away from the posterior tectum. Nasal growth cones, which must map to the posterior tectum, are resistant to it. In vitro, when posterior membranes contact temporal growth cones over their surface, filopodia and lamellipodia withdraw rapidly. This leads to loss of contact between the growth cone and the substrate, followed by collapse.

Animals↗
PubMed1990

Extracellular haemolysin of Proteus penneri coded by chromosomal hly genes is similar to the alpha-haemolysin of Escherichia coli.

Extracellular haemolysin of four Proteus penneri strains was characterized as a polypeptide of approximately 110 kD. The chromosomal DNAs of these strains cleaved with Hind III showed three fragments hybridizing with a DNA probe containing cloned haemolysin (hly) genes of Escherichia coli. The results presented here suggested that the haemolysin of P. penneri strains is chromosomally determined and similar to the alpha-haemolysin of E. coli.

Blotting, Southern↗