Regulation of RNA polymerase II transcription through re-initiation and bursting.

The regulation of RNA polymerase II (RNAPII) activity requires orchestrated responses among genomic regulatory sequences and an expansive set of proteins and protein complexes. Despite intense study over five decades, mechanistic insights continue to emerge. Within the past 10 years, live-cell imaging and single-cell transcriptomics experiments have yielded new information about enhancer-promoter communication, transcription factor dynamics, and the kinetics of RNAPII transcription activation. These insights have established RNAPII re-initiation and bursting as a common regulatory phenomenon with widespread implications for gene regulation in health and disease. Here, we summarize regulatory strategies that help control RNAPII bursting in eukaryotic cells, which is defined as short periods of active transcription followed by longer periods of inactivity. We focus on RNAPII re-initiation (i.e., a "burst" of two or more polymerases that initiate from the same promoter), with an emphasis on molecular mechanisms, open questions, and controversies surrounding this distinct regulatory stage.