Bromodomain-containing protein 4 (BRD4)

Chromatin reader protein which 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 through the whole cell cycle and provides epigenetic memory for postmitotic G1 gene transcription by preserving acetylated chromatin status and keeping 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 recruitment it to promoters: BRD4 is required to form the transcriptionally active P-TEFb complicated by displacing negative regulators such as HEXIM1 and 7SKsnRNA complicated from P- TEFb, thereby transforming it into an active form which can then phosphorylate the C-terminal domain (CTD) of RNA polymerase II. According to a report, directly acts as an atypical protein kinase and mediates phosphorylation of'Ser-2' of this C-terminal domain (CTD) of RNA polymerase II; these data nevertheless need additional evidences in vivo (PubMed:22509028).