The response of ataxia telangiectasia cells to bleomycin.

The autosomal recessive disorder, ataxia telangiectasia (AT) is characterised by cellular sensitivity to ionizing radiation. The molecular basis of this radiosensitivity is the subject of controversy. We report here that cultured fibroblasts from AT patients are also sensitive to the lethal effects of bleomycin. As with ionizing radiation, no defect has been observed in the overall rejoining of single or double-strand breaks produced by bleomycin. Since, however, only apyrimidinic (and to a lesser extent apurinic) sites and strand breaks are known to be produced by bleomycin, we tentatively suggest that AT cells are unable to rejoin a very small fraction of the total strand breaks. We attribute our inability to detect such unrejoined strand breaks to the relative insensitivity of the sucrose gradient procedures normally used to detect strand breaks.