RMP specifically binds RPB5 in vitro. Partially purified bacterial recombinant proteins were fractionated by SDS–12.5% PAGE and stained with Coomassie brilliant blue (A) or transferred onto nitrocellulose membranes for far-Western blot analysis (B). Coomassie brilliant blue staining showed that comparable amounts of GST-fused HBx, human RPB5, TBP, CTD, and GST proteins were applied. (B) The GST-RMP probe bound specifically to RPB5 but not to HBx, CTD, TBP, or GST.