Replicative DNA synthesis in permeable fibroblasts from normal individuals and ataxia-telangiectasia patients

Replicative DNA synthesis in normal human fibroblasts was inhibited by 50% when they were X-irradiated (8 Gy) and made permeable 30 min later, whereas only a slight inhibition (20%) was observed in similarly treated ataxia-telangiectasia cells. Treatment of irradiated normal cells with caffeine (2 mM) before permeabilization reversed the inhibitory effects of X-rays, buf caffeine had no effect on DNA synthesis in permeable ataxia-telangiectasia cells. Diadenosine tetraphosphate (0.1 mM) did not affect DNA synthesis in permeable normal fibroblasts.