DNA damage-induced protein sumoylation and physical association of UBE2I and PIAS1. (A) Sumo-1 immunoblot of RPMI 8226 lysates at indicated times after exposure to 10 Gy γ-radiation. (B) DNA-damage promotes induction of UBE2I and PIAS1. RPMI 8226 lysates at indicated times after exposure to 10 Gy γ-radiation were probed with antisera to either Ube2I (top) or PIAS1 (bottom). (C) Coimmunoprecipitation of PIAS1 with Ube2I. Ube2I immunoprecipitates of RPMI 8226 cells treated with 10 Gy γ-radiation show immunoreactive bands with a PIAS1 pAb (top); conversely, PIAS1 immunoprecipitates probed for MYC detected MYC-Ube2I fusion protein (20 kDa).