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Updated: Jun 8, 2025

A Rapid High-throughput Method for Mapping Ribonucleoproteins RNPs on Human pre-mRNA
Published on: December 2, 2009
Nucleolar Pol II interactome reveals TBPL1, PAF1, and Pol I at intergenic rDNA drive rRNA biogenesis
Negin Khosraviani1, V Talya Yerlici1, Jonathan St-Germain2,3
1Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
Abstract:
Ribosomal DNA (rDNA) repeats harbor ribosomal RNA (rRNA) genes and intergenic spacers (IGS). RNA polymerase (Pol) I transcribes rRNA genes yielding rRNA components of ribosomes. IGS-associated Pol II prevents Pol I from excessively synthesizing IGS non-coding RNAs (ncRNAs) that can disrupt nucleoli and rRNA production. Here, compartment-enriched proximity-dependent biotin identification (compBioID) revealed the TATA-less-promoter-binding TBPL1 and transcription-regulatory PAF1 with nucleolar Pol II. TBPL1 localizes to TCT motifs, driving Pol II and Pol I and maintaining its baseline ncRNA levels. PAF1 promotes Pol II elongation, preventing unscheduled R-loops that hyper-restrain IGS Pol I-associated ncRNAs. PAF1 or TBPL1 deficiency disrupts nucleolar organization and rRNA biogenesis. In PAF1-deficient cells, repressing unscheduled IGS R-loops rescues nucleolar organization and rRNA production. Depleting IGS Pol I-dependent ncRNAs is sufficient to compromise nucleoli. We present the nucleolar interactome of Pol II and show that its regulation by TBPL1 and PAF1 ensures IGS Pol I ncRNAs maintaining nucleolar structure and function.
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