Gamma irradiation-induced G2 arrest results in stabilization of Wee-1. HeLa cells (1.5 × 105) were synchronized by double thymidine block at G1/S and gamma irradiated with 4,000 rads following release. (A) Cells were collected at various times after gamma irradiation, stained with propidium iodide, and analyzed with a FACScan cell sorter. (B) Cell lysates were analyzed at the indicated time points with an antibody specific for Wee-1. (C) HeLa cells were transfected with siRNA to wee-1 (siWee-1) or luciferase (siLuc.) for 4 h following release and irradiation. Cells were then collected for cell cycle analysis at the indicated time points. (D) Fourteen hours after release siWee-1-transfected cell lysates were analyzed for Wee-1 expression. IR, irradiation; P.IR, postirradiation.