| Abstract: | Formation of alkaline-labile sites in DNA by S9-activated benzo a]pyrene (B a]P) and the repair of those lesions were investigated using the technique of alkaline elution in cultured Chinese hamster V79 cells. When the cells were treated with B a]P (1-5 micrograms/ml) there was negligible increase in DNA elution at pH 12.1 as compared to untreated controls. However, the elution of DNA increased at pH 12.6 with a concentration dependency, thereby indicating formation of alkaline-labile sites in DNA by B a]P. After 4 h of repair incubation the elution of DNA at pH 12.6 of B a]P (5 micrograms/ml) treated cells returned to the control levels. The half-life of alkaline-labile sites formed by B a]P was approximately 1.5 h. Inhibitors of DNA-repair synthesis, hydroxyurea (HU) and 1-beta-D-arabinofuranosyl cytosine (ara-C) when added simultaneously with S9-activated B a]P for 3 h showed an increase in elution of DNA at pH 12.1, indicating that a population of B a]P-induced DNA lesions could be removed by a rapid DNA-repair process. These results indicate that at least two kinds of DNA lesions, repairable alkaline-labile sites and rapidly repairable DNA single-strand breaks, are detected after B a]P treatment by the use of the alkaline elution procedure, by changing elution pH. |
