Cayman’s HAT Inhibitor Screening Assay provides a fast, fluorescence-based method for evaluating PCAF HAT inhibitors. The procedure requires only three easy steps, all performed in the same microplate. In the first step of the protocol, HAT is incubated with acetyl-CoA and the histone H3 peptide. During this time, HAT catalyzes the enzymatic transfer of acetyl groups from acetyl-CoA to the H3 peptide producing an acetylated peptide and CoASH. Following addition of isopropanol to stop the enzymatic reaction, CPM is added to the wells of the plate. CPM reacts with the free thiol groups present on CoASH forming a highly fluorescent product that is detected using excitation and emission wavelengths of 360-390 and 450-470 nm, respectively.