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Trimethylpsoralen was used to crosslink the extrachromosomal ribosomal DNA in nucleoli or nuclei of growing Dictyostelium discoideum cells. The DNA was extracted and was examined by spreading under denaturing conditions for electron microscopy. Intact 95,000 base ribosomal DNA molecules were seen, showing regularly spaced, single-stranded bubbles of about(More)
The structure of ribosomal chromatin in exponentially growing Friend cells, in stationary cells, and in metaphase chromosomes was studied by psoralen photocrosslinking. It is shown that in intact cells, two distinct types of ribosomal chromatin coexist in Friend cells, one that contains nucleosomes and represents the inactive copies and one that lacks a(More)
Recently, we showed for the wastewater of a large Swiss university hospital that primary DNA damage, assessed by a bacterial SOS repair assay (umuC test), could be largely assigned to a specific class of antibiotics, the fluoroquinolones (FQs) (Hartmann et al. [1998] Environ Toxicol Chem 17:377-382). In an attempt to confirm the significance of FQs for the(More)
Balbiani ring 2 (BR2) in salivary glands of Chironomus pallidivittatus and C. tentans (two sibling species of the subgenus Camptochironomus) is a favoured model system for studies of gene organization and transcript formation. Here we show that BR2 is more complex than hitherto believed, containing two 75S RNA-producing genes, BR2a and BR2b, present in(More)
The genotoxic potential of the waste water of a hospital was evaluated by the umuC test. Within 2 years over 800 native waste water samples were analysed. Genotoxic activity was found in 13% of the samples. The highest genotoxic activity occurred in the morning hours, but genotoxic samples were detected also during the day and at night. 96% of the genotoxic(More)
The photoelectric aerosol sensor (PAS) is a technique suitable for on-line monitoring of particle-bound polycyclic aromatic hydrocarbons (PPAHs). Although this is a very fast and inexpensive technique, it does not measure individual PAH species but gives a measure of the total amount of PPAHs. Because of the suitability of this sensor for air-pollution(More)
We examined the chromatin structure of a Balbiani ring (secretory protein gene) in the salivary glands of Chironomus larvae in its hyperactive state after stimulation with pilocarpine. For the inactive state of the gene an established tissue culture cell line, not expressing the gene, was used. Electron microscopy showed an RNA polymerase density of(More)
When chromatin is photoreacted with psoralen, crosslinks occur preferentially in the linker DNA between nucleosomes. The pattern of these crosslinks can be analysed by exonuclease digestion of random DNA fragments, since the exonucleases tested stop at sites of psoralen-crosslinks. Further digestion of these fragments with S1-nuclease leads to DNA fragments(More)