Ionizing radiation (IR) is known to activate multiple signaling pathways, resulting in diverse
stress responses including apoptosis, cell cycle arrest, and gene induction. IR-activated cell
cycle checkpoints are regulated by Ser/Thr phosphorylation, so we tested to see if protein
phosphatases were targets of an IR-activated damage-sensing pathway. Jurkat cells were
subjected to IR or sham radiation followed by brief 32 P metabolic labeling. Nuclear extracts
were subjected to microcystin affinity chromatography to recover phosphatases, and the …