Relation of double-stranded DNA breaks and their repair to cell death and recovery after methylnitrosourea exposure

The yield of DNA double-strand breaks (DSB) in the cells of mouse lymphosarcoma treated with nitrosomethylurea (NMU) was registered by means of elastoviscosimetry. It was shown that after short-term (7 min) treatment with NMU the lesions formed in DNA are efficiently repaired both in complete and conditioned media. After long-term (30 min) treatment DNA was only repaired in complete growth medium. The yield of the first fixed DSB after long-term NMU treatment correlated with the mean lethal dose D0. After short-term NMU treatment the first DSBs are registered in the dose range which is 4-fold higher than D0. The nature of lethal and potentially lethal lesions as well as the participation of various repair systems in the elimination of potentially lethal lesions are discussed.