PP1 PNUTS binds the “restrictor” and dephosphorylates pol II CTD Ser5 to stimulate RNA pol II transcription termination [ChIP-seq]

The restrictor complex, WDR82/ZC3H4, is the major termination factor for antisense transcription from bidirectional promoters, but its mechanism of action is poorly understood. We report that the PP1 phosphatase nuclear targeting subunit PNUTS binds to restrictor via its WDR82 subunit. AlphaFold predicts a quaternary complex, PPWZ, in which PP1-associated PNUTS and ZC3H4 both contact WDR82. A chimera comprising inactive PP1H66K fused to the C-terminal PNUTS sequences including its WDR82 binding domain binds to restrictor and acts as a dominant negative inhibitor of antisense termination and CTD Ser5 dephosphorylation. The PP1H66K-PNUTS is a substrate trap that also interacts with pol II large subunit and nuclear exosome components. Ser5 hyperphosphorylated pol II has increased processivity and pauses less frequently than total pol II. We speculate that the elevated elongation efficiency of Ser5-P pol II antagonizes early termination and that Ser5 dephosphorylation by PP1/PNUTS/WDR82/ZC3H4 is coupled to termination of antisense transcription.