This study is the first report of the full-length 3D structure of eukaryotic RNA-dependent RNA polymerase (RDR). The authors focused on the gene product of RDR2, which is involved in the biogenesis of the most abundant endogenous siRNAs in plants, which direct sequence-specific cytosine methylation and histone modification causing genomic-loci specific transcriptional silencing. They performed a series of functional analyses based on the RDR2 structure they solved, and proposed a detailed model describing how RDR2 is coupled to RNA polymerase IV for mRNA transcription and generates an antisense RNA strand to the mRNA. The precise structural and functional information of full-length RDR2 will provide the community with solid mechanistic insights into the epigenetic control of a wide variety of plant species in addition to Arabidopsis.
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