ARMC5-mediated degradation of RNA polymerase II as a last resort in the promoter-proximal pausing checkpoint [RNA-Seq]

RNA polymerase II (RNAPII) promoter-proximal pausing is an early step in the transcription cycle, which occurs alongside important events such as mRNA capping. Here, we identify a ubiquitin ligase complex, CUL3-ARMC5 (CRL3ARMC5) which is required for targeting promotor-proximally paused RNAPII for degradation. While a basal level of ARMC5-dependent RNAPII ubiquitylation/degradation occurs even in unperturbed cells, depletion of proteins regulating promoter-proximal pausing results in markedly increased ubiquitylation. We suggest that such RNAPII ubiquitylation/degradation serves as a “last resort” pathway for removing inept polymerases at a promoter-proximal pause checkpoint to avoid their release for unproductive transcript elongation. In agreement with this idea, ARMC5 knockout cells display increased levels of nascent transcription but with pre-mRNAs exhibiting capping defects. Together, our findings support a model in which promoter-proximal pausing functions as a transcription cycle checkpoint and indicate broad role for the CRL3ARMC5 ligase in RNAPII poly-ubiquitylation and degradation.