Interaction between UV light and restriction endonuclease AluI in CHO cells: a cytogenetic analysis

139 Polyploid cells were increased 3-fold in patients compared to controls. In lymphocyte cultures patients revealed an increased percentage of tetraploid mitoses (0.4%) compared to controls (0.0%). In fibroblast cultures no striking differences could be ascertained between patients and controls. Regarding the amount of aneuploid mitoses analysed in the lymphocyte cultures patients showed higher values than controls (10.5%/ 8.1%). In patients the aneuploid cells consisted of hyper- and hypoploid metaphases, whereas controls revealed only hypoploid mitoses. The percentage of structural aberrant mitoses in patients was higher than in controls (patients 6.7%/controls 5.9%). Regarding the relation of chromatid to isochromatid aberrations there were also significant differences between the two investigation groups (patients C' : C" = 1 : 10.7/ controls C' : C" = 1 : 0.5). The rate of sister-chromatid exchanges was slightly increased in patients, though without any correlation to specific fragile sites of the autosomes. Additional nonisotopic in situ hybridization with biotinylated #2-library DNA in man and chimpanzee revealed evolutionary conservation of the aphidicolin-inducible common fragile site in 2q31, which previously was discussed to be a specific breakpoint in patients suffering from systemic sclerosis. Summarizing our findings we could show that untreated patients with an autoimmune disease such as systemic sclerosis have a defect leading to misdistribution of chromosomes and nuclei and to increased chromosome breakage in the G 1 phase.

Interaction between UV light and restriction endonuclease A/ul in CHO cells: a cytogenetic analysis Restriction endonucleases (REs) induced chromosomal aberrations in mammalian cells in vitro independently of the S phase of the cell cycle. Since REs can only cut naked DNA, it is not obvious that they find such DNA in the intact chromatin. It has been proposed that REs "read" recognition sites in the chromatin by a displacement of chromosomal proteins. It has been shown that UV radiation at the wavelengths from 254 to 434 produces pyrimidine photoproducts (dimers and 6-4 adducts) and DNA-protein covalent bonds (DNA-protein cross-links) in cultured cells. In order to study the role of chromatin structure, CHO cells were irradiated with UV light (254 nm, 6 J) and post-treated with AluI (7 U) in the G 1 phase of the cell cycle. After UV irradiation the yield of AluI-induced chromosomal aberrations decreased about 50%. We speculate that the reduction of chromosome-type aberrations obtained in combinated treatments with UV and AluI, compared to the treatment with AluI alone, could be mediated by a "protective" effect of UV-induced DNA-protein cross-links against the activity of the restriction endonuclease in CHO cells.

59 Werle-Schneider, G. 1,2, M. Schwarz 2 and H.R. Glatt 1, ~ Institute of Toxicology, Mainz and 2 German Cancer Research Center, Institute of Experimental Pathology, Heidelberg (Germany) Different types of mutagenic metabolites of polycyclic aromatic hydrocarbons: initiation and promotion of enzyme-altered liver foci in rats

58 TanzareUa, C. 1, A. Antoccia 1, F. Palitti 2, M. Fiore ~ and G. Obe 3, 1 Department of Genetics and Molecular Biology, University "La Sapienza", Rome, 2 Department of Agrobiology and Agrochemistry, University of Tuscia, Viterbo (Italy) and 3 Institute of Genetics, University of Essen (Germany)

Different metabolites of polycyclic aromatic hydrocarbons such as dihydrodiol epoxides, phenol dihydrodiol epoxides, benzylic esters and quinones have been demonstrated to be mutagenic in vitro. In order to estimate the relative importance of different classes of metabolites in vivo some proximate or ultimate representatives