The conserved RNA-binding protein Seb1 promotes cotranscriptional ribosomal RNA processing by controlling RNA polymerase I progression

Transcription by RNA polymerase I (RNAPI) represents the majority of the transcriptional activity in eukaryotic cells and is associated with the production of mature ribosomal rRNAs (rRNAs). As several rRNA maturation steps are coupled to RNAPI transcription, the rate of RNAPI elongation directly influences processing of nascent rRNA, and changes in RNAPI transcription rate can result in alternative rRNA processing pathways in response to growth conditions and stress. However, factors and mechanisms that control RNAPI progression by influencing transcription elongation rate remain poorly understood. We show here that the conserved fission yeast RNA-binding protein Seb1 associates with the RNAPI transcription machinery and promotes RNAPI pausing states along the rDNA. The overall faster progression of RNAPI at the rDNA in Seb1-deficient cells impaired cotranscriptional rRNA processing and the production of mature rRNAs. Given that Seb1 also influences pre-mRNA processing by modulating RNAPII progression, our findings unveil Seb1 as a pausing-promoting factor for RNA polymerases I and II to control cotranscriptional RNA processing. CRAC (Cross-linking and Analysis of cDNA) experiment to measure nascent RNAP I transcription in wild-type and cells deficient for the Seb1 protein.