Fig. 4. Requirement of IKK in Tax-induced p100 processing. (A) Induction of p100 processing by Tax and its mutants. 293 cells were transfected with an empty vector or the indicated Tax constructs followed by analyzing the p100 processing and expression of Tax by IB. (B) Parental Jurkat (Wt), an IKKγ-deficient (γ^–/–) Jurkat derivative JM4.5.2 or an IKKγ-reconstituted JM4.5.2 [γ^–/–(IKKγ)] (Rivera-Walsh et al., 2000) was infected with retroviral vectors encoding GFP or Tax, followed by IB analysis of endogenous p100/p52 (upper panel) and infected Tax (lower panel) (lanes 1–4). In lanes 5–8, the uninfected cells were either not treated (–) or stimulated for 8 h with PMA plus ionomycin (+), followed by IB analysis of endogenous p100/p52 (upper panel) and actin (lower panel). (C) Transient transfection was performed with the parental and IKKγ-deficient Jurkat cells and the expression vectors indicated (1 µg for p100 and Tax, 0.2 µg for IKKγ, 0.8 µg for NIK; V stands for pcDNA vector). Processing of exogenous p100 was analyzed by IB.