Stable pausing by RNA polymerase II provides an opportunity to target and integrate regulatory signals

Metazoan gene expression is often regulated after the recruitment of RNA polymerase II (Pol II) to promoters, through the controlled release of promoter-proximally paused Pol II into productive RNA synthesis. Despite the prevalence of paused Pol II, very little is known about the dynamics of these early elongation complexes or the fate of short transcription start site-associated (tss) RNAs they produce. Here, we demonstrate that paused elongation complexes can be remarkably stable, with half-lives exceeding 15 minutes at genes with inefficient pause release. Promoter-proximal termination by Pol II is infrequent and released tssRNAs are targeted for rapid degradation. Further, we provide evidence that the predominant tssRNA species observed are nascent RNAs held within early elongation complexes. We propose that stable pausing of polymerase provides a temporal window of opportunity for recruitment of factors to modulate gene expression and that the nascent tssRNA represents an appealing target for these interactions. This submission includes 13 raw data files. Four samples (chromatin, soluble, mock-treated, and Rrp40-depleted) are represented by two biological replicate raw data files, while five samples (cells, DMSO, FP, mock-treated + FP, and Rrp-40depleted + FP) are represented by single raw data files.