The P-TEFb-interacting domain (PID) of BRD4 is an autonomous transactivation domain. (A) Increasing amounts of plasmids encoding the GAL4 DNA-binding domain (dbd) fused to BRD4(1209–1362), BRD4(1209–1328), or BRD4(1209–1362)(FEE1357AAA), were cotransfected with p5×GAL4-UAS-luciferase into HeLa cells. After 36 h, lysates were prepared, and luciferase levels were determined.