Altered DNA synthesis in irradiated and unirradiated ataxia-telangiectasia cells.

DNA synthesis in cells from ataxia-telangiectasia (AT) patients differs from that in normal cells in two principal ways. In unirradiated cultures, AT cells have a lower inherent rate of DNA synthesis (and, therefore, a longer S phase) than normal cells and, in cultures exposed to ionizing radiation, DNA synthesis is not inhibited as it is in normal cells; this radioresistant DNA synthesis is due to completely resistant DNA chain elongation and partially resistant DNA replicon initiation. It is probable that the defects in DNA synthesis in irradiated and unirradiated cells are related and are at least partially involved in the pathogenesis of this syndrome.