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. 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).