Figure 3.

Endogenous or exogenous β-actin is associated with RNAP II during the differentiation of HL-60 cells. (A) Nuclear extracts prepared from 5 × 10⁷ HL-60 cells untreated or treated with PMA (10 ng/ml) for 48 h were subjected to immunoprecipitation with an RNAP II antibody. The bound proteins were eluted by boiling in SDS sample buffer and separated on SDS-PAGE gel, and analyzed by Western blotting with a mouse mAb against β-actin. (B) Western blots from A were stripped and reprobed using an anti-RNAP II antibody. (C) Coimmunoprecipitation experiments and Western blot analyses were performed as described in A, except that HL-60 cells transfected with vector pAcGFP1-actin were used. Nuclear extracts were immunoprecipitated with an anti-RNAP II antibody and probed with a GFP antibody. (D) The Western blots from C were stripped and reprobed using the anti-RNAP II antibody. IP, immunoprecipitation; WB, Western blot analysis.