title: Distinct phases of siRNA synthesis in an endogenous RNAi pathway in C. elegans soma.
abstract: Endogenous RNA-directed RNA polymerases (RdRPs) are cellular components capable of synthesizing new complementary RNAs from existing RNA templates. We present evidence for successive engagement of two different RdRPs in an endogenous siRNA-based mechanism targeting specific mRNAs in C. elegans soma. In the initiation stage of this process, a group of mRNA species are chosen as targets for downregulation, leading to accumulation of rare 26 nt 5'-phosphorylated antisense RNAs that depend on the RdRP homolog RRF-3, the Argonaute ERGO-1, DICER, and a series of associated ("ERI") factors. This primary process leads to production of a much more abundant class of 22 nt antisense RNAs, dependent on a secondary RdRP (RRF-1) and associating with at least one distinct Argonaute (NRDE-3). The requirement for two RdRP/Argonaute combinations and initiation by a rare class of uniquely structured siRNAs in this pathway illustrate the caution and flexibility used as biological systems exploit the physiological copying of RNA.
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5324, USA.
authors.forename: Jonathan I
authors.initials: JI
authors.lastname: Gent
authors.forename: Ayelet T
authors.initials: AT
authors.lastname: Lamm
authors.forename: Derek M
authors.initials: DM
authors.lastname: Pavelec
authors.forename: Jay M
authors.initials: JM
authors.lastname: Maniar
authors.forename: Poornima
authors.initials: P
authors.lastname: Parameswaran
authors.forename: Li
authors.initials: L
authors.lastname: Tao
authors.forename: Scott
authors.initials: S
authors.lastname: Kennedy
authors.forename: Andrew Z
authors.initials: AZ
authors.lastname: Fire
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000201:enzymology / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D039642:Eukaryotic Initiation Factors / Q000378:metabolism; D005095:Exoribonucleases / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D034622:RNA Interference; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000096:biosynthesis*; D016601:RNA-Binding Proteins / Q000378:metabolism; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics / Q000378:metabolism*; D043244:Ribonuclease III / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D029742:Caenorhabditis elegans Proteins; D039642:Eukaryotic Initiation Factors; C530516:NRDE-3 protein, C elegans; C461645:RDE-4 protein, C elegans; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; C122185:rde-1 protein, C elegans; D012324:RNA-Dependent RNA Polymerase; C472756:RNA-directed RNA polymerase RRF-3, C elegans; C574791:RRF-1 protein, C elegans; C482202:ERI-1 protein, C elegans; D005095:Exoribonucleases; D043244:Ribonuclease III