HDAC inhibition increases PARP-1-NEDD8 trimer binding. NEDP1 KO U2OS cells were left untreated or treated with the HDAC inhibitor sodium butyrate (NaB) (10 mM) for 4 hours. Cells were harvested and lysates were incubated with recombinant Zn1-GFP or Zn2-GFP (25 nM) for 1 hour followed by immunoprecipitation with GFP-Trap. Immunoprecipitated proteins were resolved by SDS-PAGE followed by Western blot analysis with the indicated antibodies. 