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F Wohlrab

Publications and source records attributed to F Wohlrab.

At least 19 recordsLinked to original sources
PubMed1992

GC-rich flanking tracts decrease the kinetics of intramolecular DNA triplex formation.

The effect of the base composition of flanking sequences on DNA intramolecular triplex formation was investigated in negatively supercoiled plasmids. The rates of triplex formation at two oligopurine.oligopyrimidine inserts with interrupting sequences in plasmids containing AT- or GC-rich flanking sequences were compared as a function of temperature, pH, and negative superhelical density. The kinetics of the transition of linear B-DNA to triplex (also called H-DNA) were influenced by all of these factors; triplexes were formed slower in a GC-rich background than in an AT-rich background. However, at equilibrium, the same amounts of the triplexes in AT- or GC-rich contexts were formed, and the conformations adopted by (GAA)4TTCGC(GAA)4 showed the canonical intramolecular triplex as mapped with chemical probes. We propose that the GC-rich segments caused this effect by thermodynamically clamping the DNA inserts, since the dependence of kinetics on base composition disappeared in tetraalkylammonium ions which eliminate the dependence of helix-coil transitions on base composition. The dependence of the kinetics of intramolecular triplex formation on flanking sequences further strengthens the concept of the role of DNA as a dynamic participant in cellular events.

Base Sequence↗
PubMed1992

Metal ions cause the isomerization of certain intramolecular triplexes.

The influence of cations on the capacity of five oligopurine.oligopyrimidine mirror repeat sequences to adopt intramolecular triplexes (the usual H-y3 isomer and/or the rare H-y5 isomer) in recombinant plasmids was investigated. Unexpectedly, the presence of certain metal ions (magnesium, zinc, manganese, and calcium) stabilized the (GAA)4TTCGC(GAA)4 insert in the rare H-y5 when cloned into either of two different sequence backgrounds. Alternatively, either shortening or lengthening the sequence at the central interruption, which becomes the loop of the triplex, led to the formation of the canonical H-y3 under all conditions tested. Similarly, other oligopurine.oligopyrimidine mirror repeat sequences (i.e. (GAA)8 or (GGA)8) formed only the H-y3 under all experimental conditions. All triplexes were stabilized by negative supercoiling at pH 5.0; chemical probe and primer extension analyses served as critical structural tools. Hence, the nature of the central interruption sequence (the loop) of the mirror repeat is important for the stabilization of the H-y5. This region may be important for metal ion binding in the initial stages of triplex formation and thus may play a critical role in determining which isomer is formed. The possible biological role of a DNA sequence adopting three different conformations is discussed.

Cations↗
PubMed1991

The herpes simplex virus 1 segment inversion site is specifically cleaved by a virus-induced nuclear endonuclease.

Nuclear extracts from several tissue culture cell lines (human, primate, and murine) contain an endonuclease that specifically cleaves sequences at the herpes simplex virus 1 (HSV-1) segment inversion site. Mapping studies identified the preferential site of cleavage as a set of tandemly repeated dodecamers, the DR2 repeats. Endonuclease levels vary according to the proliferative state of the cell; little or no activity is detectable in extracts from quiescent cells, whereas high levels are expressed in dividing cells. Also, infection of density-arrested BSC-1 cells with HSV-1 induces a substantial increase (at least 35-fold) in endonucleolytic activity, which is first detectable at about 1 hr after infection at 32 degrees C. The elevated levels of enzyme activity then persist throughout the viral life cycle. In addition to the HSV-1 DR2 repeats, certain other G+C-rich sequences with an asymmetric distribution of purines and pyrimidines on the DNA strands and with appropriate sequences and lengths are substrates for the nuclease. These data indicate that target site recognition by the enzyme is conformation specific rather than sequence specific.

Animals↗
PubMed1991

[Victoria blue: staining properties in orthology and pathology].

The staining properties of the cationic dye Victoria Blue are summarized in consideration of the findings in the literature and own findings. Dependent on the staining conditions (with or without preoxidation of tissue sections), different structures and substances are stained by Victoria Blue. Without preoxidation elastic fibres, acid glycosaminoglycanes and DNA predominantly stained, but with preoxidation the dye stained insulin, some peptide hormones and secretion products, HBs-antigen, and lipofuscin. The chemism of the histochemical reaction is not quite understood yet.

Animals↗
PubMed1990

Morphological findings in the liver of diabetic rats after intraportal transplantation of neonatal isologous pancreatic islets.

Morphological (light microscopical, immunohistological and electron microscopical) findings in the recipient liver of rats with streptozotocin-induced diabetes, obtained 9 months after intraportal injection of neonatal isologous pancreatic islets, are described and their significance discussed. The results support the assumption of active ingrowth of nonmyelinated nerve fibers into the islet isografts. The hepatocytes surrounding the islet isografts contain--obviously owing to the influence of unusually high and locally variable concentrations of insulin--a focally increased number of enlarged mitochondria, abundant glycogen and a smaller amount of neutral fat droplets. Furthermore, hepatocytes and cells looking like hepatocytes (hepatocyte-like cells) with typically structured cytoplasmic beta (insulin) granules were found bordering the islet isografts. These results could be interpreted as an expression of artificial or nonartificial fusion of beta cells with hepatocytes, i.e. formation of hybrid cells ("in vivo hybridization"). Alternatively, they might reflect insulin uptake and storage in the hepatocytes. In addition, these findings suggest that contact between neonatal islet tissue and liver tissue could be a trigger for the in vivo transformation (modulation) of differentiated cells of similar embryonic development in the adult organism.

Animals↗
PubMed1990

[Gomori reactions in orthology and pathology].

The following four basic histochemical reactions were developed by Gomori (1904-1957): 1. Silver impregnation of reticular fibres (1937); 2. Metal salt principle for detection of hydrolytic enzyme activity (1939); 3. Silver-methenamine reaction (1946); 4. Aldehyde fuchsin reaction (1950). These reactions and their modifications have assumed growing importance to expansion of knowledge, primarily on orthological and pathobiological problems.

Histocytochemistry↗
PubMed1990

[Proliferation of beta cells after syngeneic transplantation of isolated Langerhans cells into the spleens of diabetic rats].

Syngeneic transplantation of cultured and functionally characterized neonatal islet into the spleen of streptozotocin diabetic Lewis rats resulted in long time survival up to 200 days and in plasma glucose levels lower than 9 mmol/l. The daily plasma glucose profile of transplanted rats had shown significantly above that of non diabetic control rats. 200 days after transplantation morphologically intact, insulin containing beta-cells were demonstrable in the spleen, thus demonstrating the long-term survival of functioning islet cells. Proliferation of beta-cells was shown in the transplanted islets. In addition, beta-cell clusters were found which derived from pancreatic ductules transplanted together with the isolated islets into the spleen. Mitose were visible within ductular epithelial cells. The proliferative response of islets after intrasplenic transplantation is probably the result of a long-term stimulation by slightly enhanced plasma glucose values of the transplanted acceptors compared to control animals.

Animals↗
PubMed1989

Slight changes in conditions influence the family of non-B-DNA conformations of the herpes simplex virus type 1 DR2 repeats.

The segment inversion site of herpes simplex virus type 1 contains a series of tandem repeats with a purine bias on one strand and high G + C content (DR2 repeats) capable of adopting a non-B-DNA structure under a variety of conditions. Plasmids carrying eight contiguous copies of DR2 sequences undergo a series of supercoil-driven conformational transitions resulting in different extents of relaxation at pH 5.0. These transitions depend on the presence of an appropriate concentration of divalent cations (Mg2+ and Ca2+) which seem to interact specifically with the alternate structure(s). The transitions occurred at approximately the same superhelical density for all lengths of inserts studied. However, the onset of the transition can be shifted to lower negative superhelical densities by increasing NaCl concentrations. This leads to a reduction of the cooperativity of the transition, which takes place over a range of linking isomers under these conditions. Extrapolating from these results, we established physiological conditions where the alternate DNA structure is found at negative superhelical densities as low as -0.035. The existence of non-B-DNA conformations and/or the structural transitions of these sequences located in this region of intense biological activity implies their involvement in the life cycle of the virus.

Base Composition↗
PubMed1989

Ducto-insular proliferation of beta-cells after syngeneic islet transplantation into the spleen of streptozotocin-diabetic Lewis rats.

Syngeneic transplantation of cultured and functionally characterized neonatal islets into the spleen of streptozotocin diabetic Lewis rats resulted in long time survival up to 200 d and in plasma glucose levels lower than 9 mmol/L. The daily plasma glucose profile of transplanted rats had shown significantly above that of nondiabetic control rats. Two-hundred d after transplantation, morphologically intact, insulin containing beta-cells were demonstrable in the spleen, thus demonstrating the long-term survival of functioning islet cells. Proliferation of beta-cells was shown in the transplanted islets. In addition, beta-cell clusters were found that derived from pancreatic ductules transplanted together with the isolated islets into the spleen. Mitoses were visible within ductular epithelial cells. The proliferative response of islets after intrasplenic transplantation is probably the result of a long-term stimulation by slightly enhanced plasma glucose values of the transplant acceptors compared to control animals.

Animals↗
PubMed1988

Unusual DNA structure in the regulatory region of the human papovavirus JC virus.

The human papovavirus JC virus (JCV) was analyzed for the presence of unusual DNA conformations. Recombinant plasmids containing 60% of the JCV prototype Mad-1 strain DNA were constructed and analyzed with both enzymatic and chemical probes. Fine-mapping studies revealed that the most prominent S1 nuclease-sensitive and bromoacetaldehyde-modified sites were located within the TATA boxes of each 98-base-pair tandem repeat. Further studies revealed that the S1 nuclease-sensitive site in the first TATA box (proximal to the origin) was approximately 50-fold stronger than the site in the second TATA box (distal from the origin). Deletion of the first TATA box drastically reduced the extent of bromoacetaldehyde modification in the second TATA box, whereas deletion of the second TATA box had little or no effect on the reactivity at the first TATA box. Hence, the biological and conformational role of the second TATA box remains unclear. No supercoil-induced relaxation was found, and reactions with the probes were not pH dependent. Also, fragments containing this regulatory region did not appear to be bent, although the A+T-rich segment contained a tract of eight consecutive A's. We conclude that the regulatory region of JCV contains non-B, but right-handed, DNA conformations which account for this behavior.

BK Virus↗
PubMed1988

The chemistry and biology of unusual DNA structures adopted by oligopurine.oligopyrimidine sequences.

A family of unusual DNA structures has been discovered in segments with predominantly purines in one strand (pur.pyr sequences). These sequences are overrepresented in eukaryotic DNA and have been mapped near genes and recombination hot spots. When cloned into recombinant plasmids, many pur.pyr sequences are reactive to chemical and enzymic probes that are generally specific for single-stranded DNA. An intramolecular triplex is adopted by mirror repeats of G's and A's. Other non-B DNA structures adopted by similar sequences remain to be fully clarified but may be a family of related conformations. It is likely that these unorthodox structures play an important role in the function of the eukaryotic genome.

Animals↗
PubMed1988

[The life and work of Carl Weigert (1845-1904) in Leipzig 1878-1885].

Coming from Breslau, together with J. Cohnheim (1839-1884), Carl Weigert arrived at the University of Leipzig in 1878. Here, in 1879, he was appointed extraordinary professor at the Department of Pathology. Apart from his growing commitment to autopsy and teaching, due to progressive illness of Cohnheim and the resulting involvement in management of the Department. Weigert studied topical issues of pathology, such as coagulation necrosis and pathogenesis of tuberculosis. His studies into histological staining techniques (principle of elective staining, mordant staining, staining of myelin sheaths) as well as into microtome techniques proved essential to progress in pathology and bacteriology. Weigert left the Leipzig Department of Pathology at the end of March 1885, after the Medical Faculty had failed to appoint him as the successor to Cohnheim. On the 1st of April, 1885, Weigert accepted the position of Director of Senckenberg's Pathological Institute at Frankfurt/Main.

Germany↗
PubMed1988

[Spectrophotometric studies on the binding of Victoria Blue 4R to oxidized insulin].

UNLABELLED: The empirical demonstration of insulin by the basic (cationic) dye Victoria Blue 4R (V4R; Ivić 1959) shows the character of a histochemical reaction (Wohlrab et al. 1985), while the chemistry+ of the reaction is not quite understood yet. Aim of this investigation: Will the spectral behaviour of V4R in visible light be influenced by oxidized or non-oxidized insulin? Dependent on the concentration, V4R shows in aqueous solution 2 absorption maxima (lambda = 597 and 558 nm), which represents monomers and dimers of the dye. With increasing dye concentration (200 mumol/l), V4R forms dimers and even higher polymers. Constant V4R concentration (200 mumol/l) results with increasing concentration of oxidized insulin (4 to 16 mumol/l) in a reduction of extinction, while the extinction at lambda = 558 nm (dimers) is more decreased than at lambda = 597 nm (monomers). Non-oxidized insulin has no remarkable influence on the absorption behaviour of V4R. Extinction measurements on V4R stained B-cells of islets of Langerhans after pre-oxidation of the section resulted in a main absorption maximum at lambda = 554 nm. CONCLUSION: Depending on the concentration, the dye V4R is associated with the oxidized insulin in aqueous solution, which is also indicated by the occurrence of an isobestic point in the curve behaviour. This is expressed by the establishment of a concentration-dependent equilibrium between the dye V4R and the oxidized insulin (change in the dissociation and aggregation behaviour respectively of the dye V4R). The determined main absorption maximum (lambda = 554 nm) in the biological material points in the same way to interactions between the stain and oxidized insulin.

Coloring Agents↗
PubMed1987

Reaction conditions affect the specificity of bromoacetaldehyde as a probe for DNA cruciforms and B-Z junctions.

The reaction of bromoacetaldehyde (BAA) was investigated further with recombinant plasmids containing tracts of (CG)16, in pRW756, or (CA)32, in pRW777, which adopt left-handed Z-structures under the influence of negative supercoiling. The cruciform structures adopted by the inverted repeat sequences near the replication origins of the pBR322 vectors served as internal controls for the number of unpaired bases. The extent of reaction with the B-Z junctions and the cruciforms was dependent on the reaction and analysis conditions, the method of preparation of BAA, ionic conditions, and the amount of negative supercoiling. In contrast to the previous results of Kang and Wells, B-Z junctions in addition to cruciforms do react with BAA. However, more forcing conditions are required to detect this reaction since B-Z junctions appear to be less reactive than the single stranded loops of cruciforms. The site of reaction with DNA was readily mapped with high precision at the nucleotide level. Also, a simple method is described for determining the concentration of BAA as well as its intrinsic reactivity in a given ionic medium.

Acetaldehyde↗
PubMed1987

The segment inversion site of herpes simplex virus type 1 adopts a novel DNA structure.

The 12-base pair (bp) tandem direct repeat sequences (DR2) at the joint region (a sequence) of herpes simplex virus type 1 (strain F) adopt a new type of DNA conformation under the influence of negative supercoiling. The novel conformation is dependent on the number of the DR2 repeats; the 19 mer (228 bp total) and the 14 mer (168 bp) readily form the alternate structure whereas pentamer, trimer, and dimer repeats show somewhat different properties. S1 and P1 nuclease studies reveal that the new conformation has a major structural aberration at its center and conformational periodicities which are not identical on the complementary strands. Also, the effect of salt and pH, the location of reaction with bromo- and chloroacetaldehyde, the type of sequence (direct repeat) involved, and the nature and extent of supercoil-induced relaxations demonstrate that this structure differs from previously recognized conformations including left-handed Z helices, cruciforms, bent DNA, and slipped structures. We propose the existence of a novel conformation, anisomorphic DNA, with different structures on the complementary strands which elicit a structural aberration at the physical center of the tandem sequences. Since the oligopurine X oligopyrimidine sequence may be inherently inflexible, this supercoil-induced structural change and the physical stress on these inserts in recombinant plasmids tend to deform (crack) the DR2 sequences at their centers. Possible roles for anisomorphic DNA in the functions of this segment of intense biological activity are proposed.

Acetaldehyde↗