Restoration of WT but not K921R mutant of Abl reinstates IR-induced transcriptional-independent apoptosis. (a) HeLa cells stable depleted for Abl expression were transfected with either WT or K921R-Abl mutant along with GFP cDNA constructs. 36 h post-transfection, cells were incubated with 100 μg/ml of α-amanitin or vehicle for 2 h and then either mock-treated or exposed to 4.3 Gy of IR. 48 h later, cells were then stained with PI and subjected to flow cytometry. (b) Percent sub-G1 DNA containing GFP+ cell population is graphed and mean value obtained from three independent experiments with SD is given. *P < 0.01; **P < 0.01. (c) Lysates of mock and BLM-treated cells were adjusted for equal protein content and subjected toimmunoblotting with anti-PARP (top panel) or anti-caspase-3 antibody (middle panel). Anti-tubulin immunoblotting shows equal protein loading (bottom panel).