Structural basis of INTAC-regulated transcription

For the majority of expressed eukaryotic genes, RNA polymerase II (Pol II) forms a paused elongation complex (PEC) and undergoes promoter-proximal pausing downstream of the transcription start site 1-3. The polymerase either proceeds into productive elongation or undergoes promoter-proximal premature transcription termination 4-6. It remains incompletely understood how transcription is regulated at this stage. Here, we determined the structure of PEC bound to INTAC, an Integrator-containing PP2A complex 7, at near-atomic resolution. The structure shows that INTAC partially wraps around PEC through multiple contacts, permitting the memetic nascent RNA to run into substrate-entry tunnel of the endonuclease subunit INTS11 of INTAC for cleavage. Pol II C-terminal domain (CTD) winds over INTAC backbone module through multiple anchors and is suspended above the phosphatase of INTAC for dephosphorylation. Biochemical analysis shows that INTAC-PEC association requires unphosphorylated CTD and could tolerate CTD phosphorylation, suggesting an INTAC-mediated persistent CTD dephosphorylation followed by reinforcement of the INTAC-PEC complex. Our study reveals how INTAC binds PEC and orchestrates RNA cleavage and CTD dephosphorylation, two critical events in generating premature transcription termination.