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Biomedical subjects

C Schroeder

Publications and source records attributed to C Schroeder.

At least 91 records · Page 5Linked to original sources
PubMed1984

Antiviral activity of Norakin (triperiden) and related anticholinergic antiparkinsonism drugs.

In view of the coincidence of antiviral and antiparkinsonism activities of amantadine four antiparkinsonism drugs, NorakinR (triperiden), ParkopanR (trihexyphenidyl), AntiparkinR (diethylbenzhydramine) and AkinetonR (biperiden) were tested for antiviral activity in various virus-cell systems. Norakin inhibited the replication of influenza A viruses in chick embryo fibroblast, MDCK and Ehrlich ascites tumour cells. It also inhibited the replication of measles virus in Vero cells, 50% inhibitory concentrations being 2-6 micrograms/ml. The drugs were also active against influenza B virus. Several representatives of other virus families, e.g. vaccinia, vesicular stomatitis, polio type 1 and herpes simplex type 1 viruses were insensitive to the compounds.

Animals↗
PubMed1984

DNA methylation of T3 virus ocr+ and ocr- strains in Escherichia coli cells harbouring the EcoK DNA host specificity system.

The influence of the T3 gene functions ocr+ and sam+ on the extent of phage DNA methylation in Escherichia coli K12 cells was studied by determining the proportion of 6- methylaminopurin to adenine in the purified DNA of T3 wild-type, sam- and ocr- sam- phage strains. We demonstrate that the DNA of T3 ocr- sam- mutants carries 12 methyl groups as a result of the action of the host-specificity methylase EcoK . In contrast to this the DNA of ocr+ strains is not EcoK -specifically methylated.

DNA, Bacterial↗
PubMed1983

Restriction of bacteriophage T3 and T7 ocr+ strains by the type II restriction endonuclease EcoRV.

When E. coli cells carrying the plasmid pLG13 (coding for the newly discovered type II restriction endonuclease EcoRV) are infected with phage T3 or T7, only T7 is able to replicate normally. T3 wild-type as well as its ocr- mutants are subject to DNA restriction in vivo and in vitro. The EcoRV enzyme cuts T3 DNA at 5 sites. T7 and its ocr- mutants have no EcoRV sites in their DNA. In contrast to the anti-restriction activity of the T3 and T7 ocr+ gene function against type I and III restriction enzymes, the ocr+ protein is unable to inactivate the type II restriction endonuclease EcoRV.

DNA Replication↗
PubMed1982

Influence of phage T3 and T7 gene functions on a type III(EcoP1) DNA restriction-modification system in vivo.

The ocr+ gene function (gp 0.3) of bacteriophages T3 and T7 not only counteracts type I (EcoB, EcoK) but also type III restriction endonucleases (EcoP1). Despite the presence of recognition sites, phage DNA as well as simultaneously introduced plasmid DNA are protected by ocr+ expression against both the endonucleolytic and the methylating activities of the EcoP1 enzyme. Nevertheless, the EcoP1 protein causes the exclusion of T3 and T7 in P1-lysogenic cells, apparently by exerting a repressor-like effect on phage gene expression. T3 which induces an S-adenosylmethionine hydrolase is less susceptible to the repressor effect of the SAM-stimulated EcoP1 enzyme. The abundance of EcoP1 recognition sites in the T7 genome is explained by their near identity with the T7 DNA primase recognition site.

DNA Replication↗
PubMed1982

Hemispheric differences in the neural processing of stimulus location and type: effects of selective attention on visual evoked potentials.

Hemispheric differences in a negative brain potential associated with selectively attending the location and type of stimulation were investigated. The earlier portion of this negativity (between 125 and 222 msec after stimulation) was associated with attending the location of the stimulus. It was symmetrical in the central scalp regions but was greater in the hemisphere contralateral to the attended visual field in the posterior scalp region. The latter portion of this negativity (from 222 to 272 msec after stimulation) primarily was associated wih attending one of the different types of stimuli presented at a given location and was greater over the left posterior regions of the scalp. These results were interpreted in relationship to the time-course of different types of information processing in the left and right hemisphere.

Adult↗
PubMed1982

Inhibitor studies of phage T4 wild-type and mutant DNA polymerases. II. Differential inhibition by pyridoxal 5'-phosphate.

The sensitivities to pyridoxal 5'-phosphate of phage T4 wild-type and two ts mutant DNA polymerases, L98 (mutator) and CB 121 (antimutator), were studied. The wild-type and the mutator enzyme we inhibited to an equal extent, while the antimutator enzyme was six times more sensitive. The mode of inhibition was competitive with the deoxynucleoside triphosphate substrates. The CB121 DNA polymerase had a three times lower affinity to its substrates but a twofold affinity to pyridoxal 5'-phosphate. The L98 enzyme had lower affinities to both the substrates and the inhibitor.

DNA-Directed DNA Polymerase↗
PubMed1981

Inhibitor studies of phage T4 wild-type and mutant DNA polymerases. V. A. summary of kinetic and inhibitor data.

The DNA polymerases of phage T4 wild-type, the mutator mutant L98 and the antimutator mutant CB121 were purified about 100-fold free of foreign enzyme activities interfering with the polymerase assay. The enzymes were characterized as to thermostability, exonuclease activity and kinetic data with DNA template primer, deoxythymidine 5' -triphosphate, and a mixture of all four deoxynucleoside 5' -triphosphates. The effects of eight inhibitors of DNA synthesis on the three enzymes were determined (Schroeder and Jantschak 1978 and 1980, Jantschak and Schroeder 1980) and are compared here. The most selective inhibitor, pyridoxal 5' -phosphate, interacts with the active site of the polymerases while the two least discriminating drugs, distamycin A and actinomycin D, do not directly interact with the polymerases at all. The study was intended to test whether specific enzyme inhibitors elicit a differential response in temperature-sensitive structural variants of this enzyme and whether, in principle, structural variants of virus enzymes or the respective ts- mutants in vivo are suitable as a screening system for selective antiviral agents.

DNA-Directed DNA Polymerase↗
PubMed1981

Occurrence of amantadine- and rimantadine-resistant influenza A virus strains during the 1980 epidemic.

The sensitivities to amantadine and rimantadine of influenza A virus epidemic strains were assayed by the haem-adsorption reduction test in mouse Ehrlich ascites cells in comparison with prototype strains and a rimantadine-resistant mutant. Besides a majority of sensitive strains, two relatively resistant epidemic strains were identified. The possible origin of resistant strains and their importance for medical practice are discussed.

Adamantane↗
PubMed1980

Inhibitor studies of phage T4 wild-type and mutant DNA polymerases. III. Distamycin A, actinomycin D, adriamycin, daunomycin and ethidium.

Adriamycin, daunomycin and ethidium, intercalating drugs which bind to double- as well as single-stranded DNA, inhibit phage T4 antimutator mutant CB121 DNA polymerase more strongly than the T4 wild-type and the mutator L98 polymerase. In contrast, all three enzymes are inhibited equally by distamycin A and actinomycin C. The latter two inhibitors bind only to double-stranded DNA.

Dactinomycin↗
PubMed1980

Virus adaptation to host cells: the non-classical modification of phage T3.

Bacterial virus T3 undergoes host-controlled modification which is not based on "classical" processes of DNA modification and restriction. The adsorption and thus the growth of T3 on Escherichia coli W cells (E. coli K12 derivative) decisively depends on the host strain on which the virus was previously propagated. Depending on the modification conferred to the virus by its last host, its efficiency of plating (e.o.p.) on E. coli W varies by six orders of magnitude between 10(-7) and 10(-1). This does not reflect the appearance of T3 host-range mutants, but a fully reversible modification of genotypically unchanged T3 wild-type phage. The behaviour of T3 in the described host system constitutes a second case of so-called non-classical modification and restriction (KRUGER et al. 1977, Molec. gen. Genet. 153, 107-110) of bacteriophages. Non-classical modification (protein modification) is additive to and independent of DNA modification and restriction as demonstrated with the ocr- phage T3/R7. - Furthermore, our results suggest that the adsorption specificity of T3 is determined by at least two independent genetic factors; in both of these factors T3 differs from T7.

Adaptation, Physiological↗
PubMed1980

Inhibitor studies on phage T4 wild-type and mutant DNA polymerase. IV. The substrate analog 3'-fluorothymidine 5'-triphosphate.

The deoxythymidine-5'-triphosphate (dTTP) analog 3'-fluorothymidine 5'-triphosphate (3'-FdTTP) inhibits DNA synthesis by T4 wild-type, L98 (mutator) and CB121 (antimutator) DNA polymerase. CB121 DNA polymerase is less sensitive by a factor of two than the L98 and T4+ enzymes. Inhibition is not due to incorporation of the analog into DNA. 3'-FdTTP acts competitively to the substrate dTTP. The CB121 polymerase exhibits a higher Ki to Km ratio than the other two enzymes (5.3 vs. 3.3) and thus discriminates better between the substrate dTTP and its analog 3'-FdTTP. 3'-FdTTP inhibits the polymerase-associated 3'-5' exonuclease activities to the same extent as their polymerase activities. The CB121 3'-5' exonuclease activity is suppressed only half as much by 3'-FdTTP as by dTTP. The results are discussed in relation to the role of T4 DNA polymerase and its associated 3'-5' exonuclease in determining the accuracy of DNA replication.

DNA-Directed DNA Polymerase↗
PubMed1979

Mutagenic DNA repair: insertion of nucleotides opposite non-coding template structures by a reversed 3'-5' exonuclease reaction? A hypothesis.

1. The enzymatic mechanism of mutagenic DNA repair is unknown. None of the characterized DNA polymerases is capable of polymerization past non-coding template structures. 2. A hypothesis is proposed according to which polymerization opposite non-coding template structures is catalyzed by the DNA-polymerase-associated 3'-5' exonuclease under conditions which shift the equilibrium of the 3'-5' exonuclease reaction DNAn + H2O in equilibrium DNAn-1 + dNMP to the left, i.e. to the incorporation of deoxynucleoside monophosphates. 3. Conditions which favor the incorporation of dNMP by the reversed 3'-5' exonuclease reaction include a high dNMP concentration, a coupled H2O-consuming reaction and a hydrophobic enzyme environment. 4. The statements of the hypothesis are supported by published work on the biochemistry of DNA polymerases and their associated 3'-5' exonucleases, the genetics of mutagenic DNA repair and the involvement of Escherichia coli DNA polymerase III in this process. 5. The hypothesis offers an explanation of the mutator and antimutator properties of certain genes, in particular of DNA polymerase genes, and also explains how some drugs act mutagenically during DNA replication and antimutagenically against mutagenic DNA repair.

DNA Polymerase III↗