Wild-type and mutant Tat proteins were immunoprecipitated with anti-FLAG antibody; immunocomplexes were separated by 12% SDS–PAGE and analysed by western blotting with anti-HA and anti-FLAG antibodies. (C) 35S-methionine-labeled p65 (5 µl) was incubated with in vitro translated HA-IκB-α (5 µl) in presence or absence of FLAG-Tat or FLAG-Tat R(49–57)A (5, 10 or 20 µl).