Fate of DNA lesions that elicit sister-chromatid exchanges.

Using 3-way differential staining (TWD) of sister chromatids, the fate of DNA lesions involved in sister-chromatid exchange (SCE) formation was determined in murine bone marrow cells in vivo, after treatment with either mitomycin C (MMC) or cyclophosphamide (CP). Both MMC (2.6 mg/kg b.w.) and CP (7 mg/kg b.w.) induced an SCE frequency near the expected in the 2 subsequent cell divisions, but the frequency of SCE occurring at the same locus in successive cell divisions was substantially lower than expected. The results are compared with previous data obtained after exposure to gamma-rays. A model of SCE induction is proposed.