Redundant pathways for removal of defective RNA polymerase II complexes at a promoter-proximal pause checkpoint
Daniel Blears, Jiangman Lou, Nova Fong, Richard Mitter, Ryan M. Sheridan, Dandan He, A. Barbara Dirac-Svejstrup, David L. Bentley, Jesper Q. Svejstrup
Abstract
The biological purpose of Integrator and RNA polymerase II (RNAPII) promoter-proximal pausing remains uncertain. Here, we show that loss of INTS6 in human cells results in increased interaction of RNAPII with proteins that can mediate its dissociation from the DNA template, including the CRL3 ARMC5 E3 ligase, which ubiquitylates CTD serine 5 -phosphorylated RPB1 for degradation. ARMC5-dependent RNAPII ubiquitylation is activated by defects in factors acting at the promoter-proximal pause, including Integrator, DSIF, and capping enzyme. This ARMC5 checkpoint normally curtails a sizeable fraction of RNAPII transcription, and ARMC5 knockout cells produce more uncapped transcripts. When both the Integrator and CRL3 ARMC5 turnover mechanisms are compromised, cell growth ceases and RNAPII with high pausing propensity disperses from the promoter-proximal pause site into the gene body. These data support a model in which CRL3 ARMC5 functions alongside Integrator in a checkpoint mechanism that removes faulty RNAPII complexes at promoter-proximal pause sites to safeguard transcription integrity. • Integrator targets a unique form of Ser5-phosphorylated RNAPII • Loss of functional Integrator triggers ARMC5-dependent RNAPII ubiquitylation • ARMC5 and Integrator both turn over promoter-proximal RNAPII • Simultaneous loss of INTS6 and ARMC5 is accompanied by defective transcript elongation Blears, Lou, et al . reveal that loss of functional Integrator in promoter-proximal regions is compensated for by ARMC5-dependent degradation of RNAPII. Disruption of both pathways results in transcription with high levels of elongation pausing, suggesting that promoter-proximal pausing constitutes an early transcription checkpoint for licensing of elongating RNAPII.