Fig. 2.

Functions of promoter-proximal pausing and regulation of pause duration. Promoter-proximal pausing limits the rate of new initiation by RNAPII, facilitates capping of the nascent pre-mRNA and provides a window of time for integration of external signals or stimuli. Pause duration is tightly regulated and can vary from one gene to another. The residence time of RNAPII at pause sites is driven by the balance between P-TEFb recruitment, phosphatase activities and recruitment of termination factors such as Integrator, which can promote premature termination. CTD: carboxyl-terminal domain. NELF: negative elongation factor. DSIF: DRB-sensitivity inhibitory factor. PP: protein phosphatase