BRD4, a ubiquitously expressed nuclear phosphoprotein, is a member of BET protein family. It is a human homolog of mouse MCAP and consists of 2 N-terminal bromodomains, a central ET-domain, and several kinase-like motifs in its N-terminus. It is expressed as 2 isoforms, longer variant has a C-terminus region with a praline and glutamine-rich domains. BRD4 is a chromatin-binding protein whose expression is induced in response to growth stimuli. BRD4 acts at different stages of cell cycle by interacting with proteins including RFC and SPA-1 and regulates cell growth. It also has a role in regulating chromosomal dynamics during mitosis. BRD4 functions as a cellular target for E2 protein of papillomavirus.