A novel DNA-protein complex in cultured mouse fibroblasts, strain L-P3

Effects of 4-nitroquinoline 1-oxide on the DNA-protein complex

The effects of 4-nitroquinoline 1-oxide (4NQO), a well known carcinogenic compound, on the DNA-protein complex and DNA Folding Proteins were investigated. FM3A cells were treated with 10(-6) M or 10(-5) M 4NQO for 30 min. Treatment with the 10(-6) M concentration was confirmed to cause the sedimentation of the DNA-protein complex to become slower. DNA Folding Proteins were then isolated from 4NQO-treated and untreated control cells and analyzed by SDS-polyacrylamide gel electrophoresis. No appreciable differences in the amounts of the major components of DNA Folding Proteins could be found due to 4NQO-treatment, but the 92 K protein was induced in DNA-protein complex by treatment with 4NQO.

DNA damage and repair in relation to cell killing in neocarzinostatin-treated HeLa cells

To elucidate the mechanism of the cell killing activity of neocarzinostatin on mammalian cells, the drug-induced damage of DNA and its repair were examined. Very low doses of neocarzinostatin, at which high survival of cells was observed, clearly produced single-strand breaks of DNA and decomposition of the 'DNA complex', but these damages appeared to be repaired almost completely. At higher doses of neocarzinostatin, single-strand breaks were repaired to a considerable extent while double-strand breaks seemed not to be repaired. The number of non-repairable single-strand breaks was about twice that of double-strand breaks. This implies that single-strand breaks are repaired except for those constituting double-strand breaks. Although at low levels of neocarzinostatin repair of double-strand breaks may occur, the correlation existing between the colony-forming ability of cells treated with neocarzinostatin and non-repairable DNA breakage suggests that production of a small number of critical non-repairable double-strand breaks per cell may be responsible for the cell killing activity of the drug.