Tax oncoproteins interact with Gβ subunits. (A-B). HEK 293T cells were transfected with Flag-Gβ1, Flag-Gβ2, Flag-Gβ5, and HTLV-1 Tax expression constructs, as indicated. Forty-eight hours after transfection, cells were lysed and protein expression was verified by immunoblotting using anti–Tax-1 and anti-Flag–specific antibodies. Lysates were immunoprecipitated using the M2 Flag–specific antibody. Immunoprecipitated proteins were analyzed by SDS-PAGE and immunoblotting using an anti–HTLV-1 Tax antibody. (C) Lysates from MT4, Tesi, Jurkat, or Tax-1–transfected 293T cells were immunoprecipitated using an anti-Gβ or a control antibody. Immunoprecipitated proteins were analyzed by Western blot using an anti–HTLV-1 Tax antibody. (D) Lysates from HeLa or Jurkat cells were mixed with equal amounts of GST-Tax_HTLV-1 or GST alone bound to glutathione-Sepharose beads. After incubation, the precipitated proteins were analyzed by Western blot using an anti-Gβ antibody. (E) The Gβ2γ4 complex was synthesized in vitro using rabbit reticulocyte lysates in the presence of ³⁵S-labeled methionine and cysteine. Lysates were mixed with equal amounts of GST-Tax_HTLV-1, GST-Tax_HTLV-2 fusion proteins, or GST alone bound to glutathione-Sepharose beads. After incubation, the protein complexes were separated by SDS-PAGE, and ³⁵S- Gβ2γ4 was visualized by autoradiography. (F) HEK 293T cells were transfected with Flag-Gβ2 and BLV Tax expression constructs, as indicated. Forty-eight hours after transfection, cells were lysed and protein expression was verified by immunoblotting using anti-Tax and anti-Flag–specific antibodies. Lysates were immunoprecipitated using the M2 Flag-specific antibody. Immunoprecipitated proteins were analyzed by SDS-PAGE and immunoblotting using an anti–BLV Tax antibody.