Chromatin reader that recognizes and binds hyperacetylated chromatin and plays a role in the regulation of transcription, probably by chromatin remodeling and interaction with transcription factors (PubMed:18406326, PubMed:27105114). Regulates transcription by promoting the binding of the transcription factor GATA1 to its targets (By similarity). Interacts (via bromo domain 1) with GATA1 acetylated at 'Lys-312' and 'Lys-315'. Interacts (via bromo domain 1) with GATA2 acetylated on lysine residues (By similarity). Interacts (via bromo domains) with acetylated lysine residues on the N-terminus of histone H2A, H2B, H3 and H4 (in vitro). Detected on chromatin. Ubiquitous. The Bromo domains specifically recognize and bind acetylated histones. A chromosomal aberration involving BRD3 is found in a rare, aggressive, and lethal carcinoma arising in midline organs of young people. Translocation t(15;9)(q14;q34) with NUTM1 which produces a BRD3-NUTM1 fusion protein. Extended N-terminus.