HDAC inhibition increases PARP-1-NEDD8 trimer binding. NEDP1 KO U2OS cells were transfected with GFP or GFP fused to the first two zinc finger domains of PARP-1 (GFP-Zn1+2). 24 hours later, cells were left untreated or treated with the HDAC inhibitor sodium butyrate (NaB) (10 mM) for 4 hours. Cells were harvested and immunoprecipitation was performed on the lysates with GFP-Trap. Immunoprecipitated proteins were resolved by SDS-PAGE followed by Western blot analysis with the indicated antibodies. 