AT cells are extremely sensitive to ionizing radiation. Since the AT gene has homology to phosphatidylinositol 3 kinases(P13-kinases),wortman nm,a specificinhibitorofPI 3-kinase,wasusedtodetermineif P13-kinase activity regulates radiation sensitivity. Human and murine cells exposed to wortmannin alonedid not display significant cytotoxicity. Wortmanmn in combination with radiation was an effect...