RT Journal Article SR Electronic T1 Co-surveillance of ribosomal RNA by the exosome complex and nucleolar RNAi in C. elegans JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.11.23.395020 DO 10.1101/2020.11.23.395020 A1 Shimiao Liao A1 Xiangyang Chen A1 Ting Xu A1 Qile Jin A1 Zongxiu Xu A1 Demin Xu A1 Xufei Zhou A1 Chengming Zhu A1 Shouhong Guang A1 Xuezhu Feng YR 2020 UL http://biorxiv.org/content/early/2020/11/24/2020.11.23.395020.abstract AB Eukaryotic cells express a wide variety of endogenous small regulatory RNAs that function in the nucleus. We previously found that erroneous rRNAs induce the generation of antisense ribosomal siRNAs (risiRNAs) which silence the expression of rRNAs via the nuclear RNAi defective (Nrde) pathway. To further understand the biological roles and mechanisms of this class of small regulatory RNAs, we conducted forward genetic screening to identify factors involved in risiRNA generation in Caenorhabditis elegans. We found that risiRNAs accumulated in the RNA exosome mutants. risiRNAs directed a NRDE-dependent silencing of pre-rRNAs in the nucleolus. In the presence of risiRNA, NRDE-2 accumulated in the nucleolus and colocalized with RNA polymerase I. risiRNA inhibited the transcription elongation of RNA polymerase I by decreasing RNAP I occupancy downstream of the site of RNAi. Meanwhile, exosome mislocalized from the nucleolus to nucleoplasm in suppressor of siRNA (susi) mutants, in which erroneous rRNAs accumulated. These results establish a novel model of rRNA surveillance by combining ribonuclease-mediated RNA degradation with small RNA-directed nucleolar RNAi system.Competing Interest StatementThe authors have declared no competing interest.