biostudies-literatureUnknownRoche BNIGMS NIH HHSIn nature, most cells exist in a quiescent G₀ state in which cellular homeostasis must be rigorously maintained in the absence of cell division. Non-coding RNAs are prevalent in G₀ and are important regulators of development and differentiation, but their function in quiescence is unclear. Here, we identify pre-rRNA as a direct target of the RNase III enzyme Dicer specifically in quiescence. Dicer is physically present at the rDNA, and improper rRNA processing in mutants results in a nucleolar stress response involving a novel <i>trans</i>-acting non-coding RNA (RiboCop) in complex with the highly conserved proteins Enp2/NOL10 and RNase H1. RiboCop is complementary to unprocessed pre-rRNA and triggers rDNA repeat silencing via Sir2, RENT, and histone H3-lysine-9 (H3K9) methylation. Thus RiboCop silences rDNA specifically during dormancy, when silencing of non-functional rRNA becomes essential.bioRxiv : the preprint server for biology2025.09.16.676644https://www.ebi.ac.uk/biostudies/studies/S-EPMC12458480biostudies-literatureRiboCop surveils pre-rRNA processing by Dicer in cellular quiescence.PMC12458480R35 GM144206P20 GM104360Roche BMartienssen RAfalseRiboCop surveils pre-rRNA processing by Dicer in cellular quiescence.In nature, most cells exist in a quiescent G₀ state in which cellular homeostasis must be rigorously maintained in the absence of cell division. Non-coding RNAs are prevalent in G₀ and are important regulators of development and differentiation, but their function in quiescence is unclear. Here, we identify pre-rRNA as a direct target of the RNase III enzyme Dicer specifically in quiescence. Dicer is physically present at the rDNA, and improper rRNA processing in mutants results in a nucleolar stress response involving a novel <i>trans</i>-acting non-coding RNA (RiboCop) in complex with the highly conserved proteins Enp2/NOL10 and RNase H1. RiboCop is complementary to unprocessed pre-rRNA and triggers rDNA repeat silencing via Sir2, RENT, and histone H3-lysine-9 (H3K9) methylation. Thus RiboCop silences rDNA specifically during dormancy, when silencing of non-functional rRNA becomes essential.2025-01-01T00:00:00Z2025 Sep2026-05-04T03:16:14.608Z2026-05-04T03:13:29.78ZS-EPMC124584804100080910.1101/2025.09.16.676644