The acetylation of histone lysine residues plays a crucial role in the epigenetic regulation of gene transcription. A bromodomain is a protein domain that recognizes acetylated lysine residues such as those on the N-terminal tails of histones. This recognition is often a prerequisite for protein-histone association and chromatin remodeling. These domains function in the linking of protein complexes to acetylated nucleosomes, thereby controlling chromatin structure and gene expression. Thus, bromodomains serve as “readers” of histone acetylation marks regulating the transcription of target promoters. BRD3 binds hyper-acetylated chromatin and plays a role in the regulation of transcription, probably by chromatin remodeling and interaction with transcription factors. It regulates transcription by promoting the binding of the transcription factor GATA1 to its targets and transcription of the CCND1 gene. A chromosomal aberration involving BRD3 was found in a rare, aggressive, and lethal carcinoma arising in midline organs of young people.