Coimmunoprecipitation.

For coimmunoprecipitation, 10 µl of protein G-magnetic beads (Bio-adembead, Ademtech) was used for immunoprecipitation. Then, portions (1 µg) of anti-HEXIM1 antibodies (rabbit, A303-113A; Béthyl) were bound to the beads in phosphate-buffered saline (PBS) with bovine serum albumin (5 mg/ml) for 2 h at 4°C with rotation. Next, 200 µg of whole-cell extract was incubated with bead-antibody complex for 2 h at 4°C with rotation. After two washes with 100 mM salt, two washes with 150 mM salt, and one wash with 100 mM salt, the beads were boiled in 2× Laemmli buffer and loaded onto an SDS-PAGE gel.