Tax ubiquitylation mediates IKK binding and nuclear translocation of RelA. (A) HeLa cells were transfected with wild-type Tax, Tax-Ub, Tax K4-8R, or Tax K4-8R-Ub. After immunoprecipitation with anti-Tax mab, recovered proteins were blotted with anti-Tax, anti-IKKα, anti-IKKβ, or anti-IKKγ antibodies, as indicated. (B) HeLa cells were transfected as in panel A and stained by dual immunofluorescence with anti-Tax (green) and anti-RelA (red) antibodies. The percentage of nuclear translocation of RelA in Tax-positive cells is indicated. (C) Jurkat cells were cotransfected with the NF-κB-Luc (▪) or the HTLV-LTR-Luc (▨) reporters, renilla luciferase, and either Tax plasmid. Activity of the wild-type protein was set to 100%.