Detection of genotoxic activity in native hospital waste water by the umuC test.

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 waste water samples revealed a genotoxic potential without growth inhibition of test bacteria monitored as OD600, in the same way as antineoplastic drugs like mitomycin C or cisplatin. 4% of the genotoxic waste water samples showed combined cytotoxic and genotoxic activities as seen in control experiments using glutaraldehyde containing disinfectants and certain antibiotics.

Two different chromatin structures coexist in ribosomal RNA genes throughout the cell cycle.

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 repeating structure and corresponds to the transcribed genes. A single gene copy is either in one or the other chromatin state. The relative amounts of the two types of structures are similar in interphase and metaphase, however, their run-on activities differ significantly. This suggests that the two states of chromatin are maintained independently of the transcriptional process and that they are stably propagated through the cell cycle.