siRNA screen of CB components identifies large ribosomal subunit proteins that increase CB number. (A) Table of siRNA hits listed by Gene ID that increase CB number and the PE (percent effect) value. Large ribosomal subunit and ribosome biogenesis proteins are highlighted in teal. (B) Nucleolar and ribosomal proteins identified in LFQ comparing coilin-APEX2 relative to APEX2-NLS. Known CB proteins are labeled and colored orange, known dual CB and nucleolar proteins are colored cyan, new significant nucleolar protein hits are colored purple, and new significant ribosomal protein hits are colored pink. (C) Structure of human 60S subunit in complex with Tetracenomycin X (PDB ID: 6Y6X). Selected ribosomal proteins are shown as ribbons, other ribosomal proteins and rRNAs are shown as a white surface. Proteins found to affect CB number (RPL13, 14, 24, 7A, and 8) are colored orange. The protein that did not show an effect (RPL15) on CB number upon knockdown is colored marine and mostly buried. Two additional surface ribosomal proteins (RPL6 and RPL17) not enriched in proximity biotinylation are colored cyan. (D) Representative images of the top three hits showing an increase in CBs per nucleus (siANLN, siRPL14, and siRPL24). Immunofluorescent staining shows α-coilin antibody in magenta and α-nucleophosmin antibody in cyan. Scale bars = 10 µm. Histograms for each hit quantifying the number of CBs per nucleus from their respective well and plate in the screen shown in teal with siNT control in light grey (12 fields of view/well). (E) DNA content analysis. Representative histograms of Hoechst log₂ integrated intensity in siNT, siANLN, and siRPL14 normalized to siNT control. G0/G1 phase (0.75–1.25) highlighted and quantified in orange, S phase (1.25–1.75) in white/black font, G2/M phase (1.75–2.25) highlighted and quantified in purple, >4N (>2.5) highlighted and quantified in teal.