Histone acetyltransferases (HATs) enzymes regulate the acetylation of histones and non-histone proteins. The acetylation of the e-amino groups of lysine residues present at histone tails correlates largely with transcriptional activation, but it is also involved in DNA replication, DNA repair and protein–protein interactions. HATs have major roles in the control of cell fate and their misregulation is involved in the development of some human tumors. The p300/CBP-associated factor (pCAF) acetylates specific lysines on the N-terminal tails of histones H3 and H4.The SensoLyte® HAT (pCAF) Assay Kit provides a convenient protocol for screening of enzyme inhibitors and for continuous assay of pCAF activity. After incubation with acetyl CoA and histone H3 (1-21) peptide the pCAF enzyme generates acetylated H3 peptide and CoASH. The fluorogenic substrate reacts with thiol groups of CoASH and produces an increase of the fluorescence that can be detected at excitation/ emission=389nm/513nm.