DDX1 forms different protein complexes with Nullbasic and Rev. A. HEK293T cells were transfected with either empty vector (pcDNA 3.1) alone, Nullbasic (NB)-FLAG alone, Rev alone or co-transfect NB-FLAG with Rev as indicated. Endogenous DDX1, NB-FLAG and their binding partners were immunoprecipated with anti-DDX1 and anti-FLAG beads. Cell lystes and immunoprecipated proteins were separated by SDS-PAGE and target proteins were detected using anti-FLAG, anti-DDX1 and anti-Rev antibodies. B. HEK293T cells were transfected with empty vector or Tat-FLAG as indicated. Target proteins were detected using anti-FLAG, anti-DDX1 after immunoprecipitation using anti-DDX1, anti-FLAG beads or with beads alone. The figures are representative of 3 independent experiments.