Homologous recombination (HR) is essential for faithful repair of DNA lesions yet must be kept in check, as unrestrained HR may compromise genome integrity and lead to premature aging or cancer. To limit unscheduled HR, cells possess DNA helicases capable of preventing excessive recombination. In this study, we show that the human Fbh1 (hFbh1) helicase accumulates at sites of DNA damage or repl...

Tests for genotoxic or mutagenic effects of chemicals have prompted efficient biostatistical methods for the quantification of dose-response data, especially from the Ames Salmonella/microsome assay. A decision about the genotoxicity of a compound is, however, always based on several assays, and results from multiple or repeated genotoxicity assays have to be combined either qualitatively or, e...

Because mutagens typified by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) observed in cooked foods are widely consumed, detailed studies of their biochemical and biological properties including carcinogenicity are most important. IQ induces unscheduled DNA synthesis in liver cells, which when taken together with its powerful mutagenicity in the Salmonella typhimurium test system, predicts carci...

The effect of certain procarcinogens, among which demethylnitrosamine (DMN) is included, has been difficult to detect in several short-term assays. An alternative system, in which DMN effects could be easily quantitated, might be useful in studies of chemical carcinogenesis and environmental contamination. To develop such a system, we tested the possibility of measuring the amount of breakage p...

The Fusarium moniliforme mycotoxins--fusarin C, fumonisin B1, moniliformin and bikaverin--were evaluated for genotoxicity by their ability to induce unscheduled DNA synthesis (UDS) in primary rat hepatocytes. Isolated hepatocytes were exposed to several concentrations of moniliformin (5.0-500 microM), bikaverin (1.0-500 microM), fumonisin B1 (0.5-250 microM), or fusarin C (1.0-100 microM). Afla...

Chronic infection with hepatitis B virus (HBV) is one of the major etiological factors in the development of human hepatocellular carcinoma. Transgenic mice that express the HBV X protein (HBx) have previously been shown to be more sensitive to the effects of hepatocarcinogens, although the mechanism for this cofactor role remains unknown. The ability of HBx to inhibit DNA repair in transiently...

Since the capacity for DNA repair relative to other cellular processes is an important parameter relevant to mutagenesis, carcinogenesis, and also aging, its assessment should preferably be carried out in intact animals. For this reason we developed an autoradiographic technique for measuring DNA repair directly in vivo. By this method unscheduled DNA synthesis (UDS) can be detected quantitativ...

continuous labelling of callus with h-thymidine results in intermittent peaks of h-dna per chloroplast, showing synchrony of division. the increase in h-dna could be due to several replication rounds, and the drop to successive plastid divisions without intervening dna synthesis. the level of dna-binding proteins in the chloroplast parallels the peaks of plastidal dna synthesis; such proteins c...

Human cells that lack O6-alkylguanine DNA alkyltransferase (AT) activity can remove O6-butylguanine (O6-nBuG) produced in cellular DNA by exposure to N-n-butyl-N-nitrosourea as determined by radioimmunoassay of enzyme digests of DNA. Fibroblasts from xeroderma pigmentosum (XP) complementation groups A and G that show less than 5% unscheduled DNA synthesis following exposure to UVC failed to rem...

N-Diazoacetylglycine amide, a diazochetoalkane, has been studied in vitro for DNA damage and repair in cells of a cloned subline from a BALB/c mouse. To our present knowledge, none of these compounds have been investigated for such activities. At nontoxic levels, a prolonged dose-dependent unscheduled DNA synthesis was observed by autoradiography. DNA damage was studied by sedimentation through...