Chromatin reader protein that recognizes and binds acetylated histones and plays a key role in transmission of epigenetic memory across cell divisions and transcription regulation. Remains associated with acetylated chromatin throughout the entire cell cycle and provides epigenetic memory for postmitotic G1 gene transcription by preserving acetylated chromatin status and maintaining high-order chromatin structure. During interphase, plays a key role in regulating the transcription of signal-inducible genes by associating with the P-TEFb complex and recruiting it to promoters (By similarity). Associates with acetylated chromatin. Widely expressed. Detected at all stages tested, including the fertilized egg stage (at protein level). Present in the fertilized egg before mid-blastula transition, and is expressed ubiquitously at relatively high levels from gastrulation to mid-somitogenesis stages. At the 20-somite stage, expression starts to decrease in the notochord, but remains high in the head and central nervous system. This expression pattern persists until approximately 24 hours post-fertilization (hpf). At 48 hpf, expression is dramatically reduced in the posterior part of the body, and becomes restricted to the head area. The 2 bromo domains mediate specific binding to acetylated histones. The exact combination of modified histone tails required to recruit brd4 to target genes is still unclear. The first bromo domain has high affinity for acetylated histone H4 tail, whereas the second bromo domain recognizes multiply acetylated marks in histone H3 (By similarity).