Conserved protein Seb1 that interacts with RNA polymerase II and RNA is an antipausing transcription elongation factor

Maturation of protein-coding precursor messenger RNA (pre-mRNA) is closely linked to RNA polymerase II (Pol II) transcription. However, the mechanistic understanding of how pre-mRNA processing is coordinated with transcription remains incomplete. Conserved proteins interacting with the C-terminal domain of the largest catalytic subunit of Pol II and nascent RNA (CID-RRM factors) were demonstrated to play a role in pre-mRNA 3'-end processing and termination of Pol II transcription. Here, we use a fully reconstituted system to demonstrate that the fission yeast CID-RRM factor Seb1 acts as a bona fide elongation factor. Our analyses show that Seb1 exhibits context-dependent regulation of Pol II pausing, capable of either promoting or inhibiting pause site entry. We propose that CID-RRM factors coordinate Pol II transcription and pre-mRNA 3'-end processing by modulating the rate of Pol II transcription.