A bromodomain (BRD) is an approximately 110 amino acid protein domain that can recognize and bind to the acetylated lysine residues, such as the N-terminal tails of histones. The bromodomain itself adopts an all-α protein fold, a bundle of four alpha helices. 

Bromodomains, as the "readers" of histone code, are responsible in transducing the signal carried by acetylated lysine residues and translating it into various normal or abnormal phenotypes. With the development of small molecule bromodomain inhibitors, the role of bromodomains in translating a deregulated cell acetylome into disease phenotypes was recently unveiled.