Eukaryotic chromatin is well organized,both spatially and temporally,with complexes composed of genomic DNA,histone proteins,and non-histone proteins.The amino-terminus of histone tails can be modified through acetylation,which relaxes chromatin and provides space for transcription factors (TFs) to regulate gene transcription.One particular protein domain,the bromodomain,has been identified to specifically bind acetyl-lysine residues at the N-terminus of histone proteins in vivo and in vitro.A hydrophobic pocket formed by the ZA and BC loops of bromodomain-containing proteins (BCPs) is responsible for acetyl-lysine recognition and binding specificity.