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Biomedical subjects

B Auer

Publications and source records attributed to B Auer.

67 records · Page 4Linked to original sources
PubMed1982

Intracellular distribution of DNA topoisomerase I in fibroblasts from patients with Fanconi's anaemia.

The activity of DNA topoisomerase I(DNA nicking-closing enzyme) was analysed in cytoplasmic and nuclear extracts of six independently derived Fanconi and four normal fibroblast cell lines. In all experiments the total cellular activity was predominantly found in the nuclear extracts (88-100%). In addition, a minor proportion of the enzyme (up to 12%) was randomly present in some of the cytoplasmic fractions of both Fanconi and normal fibroblasts. These results indicate that Fanconi's anaemia is probably not due to or accompanied by a maldistribution of topoisomerase I between nuclei and cytoplasm.

Anemia, Aplastic↗
PubMed1982

Repair rate in human fibroblasts measured by thymine dimer excorporation.

The UV photoproduct, thymine dimer (-TT), is excorporated with a remarkably low rate from the DNA of human fibroblasts grown in cell culture. An UV dose of 18 J/m2 creates 0.045% -TT (related to thymine). Within the first two days of repair logarithmically growing and quiescent fibroblasts exhibit the same repair rates; thereafter, the proportion of -TT/T is lower in growing cells due to recovery of DNA replication. Only about 50% of the lesions are excised within 24 h. In quiescent cells, 13% of the thymine dimers originally present can be detected as late as a week after UV-irradiation. Two distinct first-order rate constants indicate that approximately half of the dimers are less accessible to repair. Repair measured by the nucleoid decondensation technique corresponds to the faster repair rate, whereas the slow repair rate cannot be detected by this method. Saturation of repair is found beyond 27 J/m2. The remarkably slow rate of excision indicates that thymine dimers are not lethal lesions in human fibroblasts.

Cells, Cultured↗
PubMed1982

A sensitive radioimmuno assay for thymine dimers.

A sensitive radioimmuno assay (RIA) method for detection of the UV photoproduct, thymine dimers (TT) has been developed. The limit of detection of this method is 6 X 10(-14) mol or 15 pg thymine dimer. It is highly specific: A structurally similar compound such as uridine dimer (UU) interferes with the detection of thymine dimers only when it is 53,000-fold or more in molar excess. Since this RIA method does not require the use of labeled DNA, it represents a considerable improvement for repair studies with radiation-sensitive cells.

Evaluation Studies as Topic↗
PubMed1979

Is the DNA of virus T7 methylated?

DNA modification of T7 wild type and of T7 M-mutants was studied by determining the percentage of 5-methylcytosine (5MC)/cytosine (C) and N6-aminopurine (6MA)/adenine (A) and by evaluating the plating efficiencies of restriction-sensitive T7 M-mutants on modifying and non-modifying host strains. Only 0.03% adenine and 0.02% cytosine were methylated in the DNA of T7 wild type as well as in T7 M-mutants, which was independent of the host DNA methylation (30- to 50-fold higher). The restriction of T7 M-mutants, determined from the plating efficiencies, was not altered on modifying or non-modifying hosts. These results indicate that host-specific modification is blocked during T7 development and that this is not due to the M-protein.

Adenine↗
PubMed1979

Development of Escherichia coli virus T1: escape from host restriction.

The bacterial virus T1 grows interchangeably on different Escherichia coli strains (C, B, and K). This implies that T1 has an efficient mechanism to overcome the host restriction barrier. The DNA of T1 was found to be methylated independently of the hosts. The percentage of N6-methyladenine varied from 1.6 to 1.8, and the 5-methylcytosine content varied from 0.1 to 0.4%. In contrast, the range in percentage of N6-methyladenine and 5-methylcytosine found in the hosts was 0.7 to 2.4 and 0.0 to 1.1, respectively.

Coliphages↗
PubMedDate not supplied

Escherichia coli bacteriophage T1 DNA methyltransferase appears to interact with Escherichia coli enolase.

Infection of Escherichia coli cells with bacteriophage T1 induces synthesis of a bacteriophage-specific DNA methyltransferase (M.EcoT1, EC No: 2.1.1.72) with a specificity for adenine residues in the sequence 5'-GATC-3'. Purification of M.EcoT1 allowed the determination of the coding sequence of the gene (Schneider-Scherzer et al., 1990). The peptide of the entire coding sequence was over-expressed as a histidine-hexapeptide tagged protein in E. coli. Affinity purification using a Ni2+ chelating (Ni-NTA) resin yielded a recombinant enzyme with almost the same enzymatic properties as the protein purified from T1 infected E. coli cells. Interestingly, in both purification procedures, a protein with a molecular weight of 50000 was found to copurify with M.EcoT1. The N-terminal amino acid sequence identified these proteins in both cases as E. coli enolase (EC No: 4.2.1.11).

DNA↗