Little information is available on the effects of UVA (320-400 nm radiation) on transcription. We examined the effect of UVA on RNA synthesis in isolated chicken liver nuclei. Nuclei in air or nitrogen were irradiated with UVA, and the RNA synthesis induced by endogenous RNA polymerase was estimated under conditions in which little or no initiation occurs. Incorporation of [³H]UMP into the acid-insoluble fraction was used as the measure of RNA synthesis in the nuclei. In air the amount of synthesized RNA decreased with increasing UVA fluence. In contrast, in nitrogen UVA had little effect on RNA synthesis. Sodium azide and histidine, which effectively scavenge singlet oxygen (¹O₂) as well as hydroxyl radicals (·OH), protected the nuclei from inhibition of RNA synthesis; whereas, sodium formate and dimethyl sulfoxide, both of which much more effectively scavenge ·OH than ¹O₂ had no protective effect. These findings provide a strong indication that ¹O₂ is involved in the inhibition of RNA synthesis. In addition, RNA polymerase II-dependent synthesis (in the nucleoplasm) was much more sensitive to UVA than RNA polymerase I-dependent synthesis (in the nucleolus).

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An N₂O-saturated aqueous solution containing 2''-dG and the spin trap agent PBN was examined by ESR and HPLC-ECD methods after X irradiation. ESR examination showed that the ESR spectrum obtained consisted of signals due to the PBN-OH and PBN-H adducts. The signal intensity of PBN-H adducts was larger in the presence of 2''-dG than in the absence of 2''-dG, while that of PBN-OH adducts was smaller in the presence of 2''-dG than in the absence of 2''-dG. When the OH-radical-induced 8-oxodG was measured by HPLC-ECD, the yield of 8-oxodG was found to be enhanced about twofold in the presence of PBN. By contrast, usual OH-radical scavengers (DMSO, sodium formate and mannitol) inhibited the formation of 8-oxodG beyond expectation. The enhancement of the yield of PBN-H adducts by 2''-dG and the enhancement of the 8-oxodG formation by PBN were explained by the electron transfer and subsequent proton transfer reactions from OH-radical-induced guanine-N7 radicals to PBN to form 8-oxodG and PBN-H. The present study led us to conclude that PBN reacted with the precursor radical of 8-oxodG to accelerate the formation of 8-oxodG, while OH-radical scavengers reacted with it to diminish the formation of 8-oxodG.

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We determined 46 spontaneous mutations occurring in the cyclic AMP receptor protein gene (crp) on the chromosomal DNA of Escherichia coli by the use of PCR cloning. Of 24 base substitutions, 17 were transversions and 7 transitions including all types of base substitutions. The frequency of the changes of A:T base pairs was similar to that of G:C pairs, suggesting that A:T pair is also a target for base substitution. Frameshifts including seven -1 and four +1 frameshifts occurred at the sites of a run of identical bases. Deletions extending 18 and 172 bases occurred at the sites where the deleted sequences were flanked by short repeated sequences at the junction. The insertions of IS2 element or its inverted sequence were detected in two and six mutations, respectively. The assay system of the mutation used here is available for the determination of the mutational spectrum of base substitutions.

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Lethal effects of ⁶⁰Co γ-rays, UV light, and mitomycin C on two kinds of bacteria, Halobacterium salinarium which grows in highly concentrated salt media and Thiobacillus intermedius which requires reduced sulfur compounds, were studied and compared with those on Escherichia coli B/r. D₃₇ values for H. salinarium, T. intermedius and E. coli B/r were 393, 150, and 92 Gy, respectively, by exposure to ⁶⁰Co γ-rays. They were 212, 38, and 10 J/m², respectively, by exposure to UV light and 2.36, 0.25, and 0.53 μg/ml/h, respectively, by exposure to mitomycin C. Against these agents, H. salinarium was much more resistant than T. intermedius and E. coli B/r.

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This study evaluated synthetic trehalose dicorynomycolate (S-TDCM), an immunomodulator, for its survival enhancing capacity and behavioral toxicity in B6D2F1 female mice. In survival experiments, mice were administered S-TDCM (25-400 μg/mouse i.p.) 20-24 hr before 5.6 Gy mixed-field fission-neutron irradiation (n) and γ-photon irradiation. The 30-day survival rates for mice treated with 100-400 μg/mouse S-TDCM were significantly enhanced compared to controls. Toxicity of S-TDCM was measured in nonirradiated mice by locomotor activity, food intake, water consumption, and alterations in body weight. A dose-dependent decrease was noted in all behavioral measures in mice treated with S-TDCM. Doses of 100 and 200 μg/mouse S-TDCM significantly reduced motor activity beginning 12 hr postinjection with recovery by 24 hr. A dose of 400 μg/mouse significantly decreased activity within the first 4 hr after administration and returned to control levels by 32 hr following injection. Food and water intake were significantly depressed at doses of 200 and 400 μg/mouse on the day following drug administration, and were recovered in 24 hr. Body weight was significantly decreased in the 200 μg/mouse group for 2 days and in the 400 μg/mouse group for 4 days following injection. A dose of 100 μg/mouse effectively enhanced survival after fission-neutron irradiation with no adverse effect on food consumption, water intake, or body weight and a minimal, short-term effect on locomotor activity.

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X-ray-induced neoplastic transformation has been studied in Syrian hamster embryo cells. Unirradiated cells had a limited life span, whereas the irradiated cells escaped senescence, showed altered morphology, and acquired anchorage-independence and tumorigenicity in a stepwise manner during successive transfers after irradiation. Multiple genetic changes may be associated with the expression of various transformed phenotypes. In fact, sequential alterations of various chromosomes were required for the malignant progression of irradiated cells. Oncogene activation was examined by the NIH3T3 transfection assay, no detectable changes having been identified so far. The only difference in oncogene expression detected was the augmented expression of the c-myc gene which was observed consistently. These findings indicate the multistep nature of X-ray-induced neoplastic transformation. Although the molecular changes involved in these process are still to be elucidated, recent studies have indicated that the instability induced by irradiation inherited through the progeny of irradiated cells is associated with those changes. This genetic instability provides a new way with which to elucidate the multistep process of radiation oncogenesis. The predicted mechanism and future studies are discussed.

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