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Posttranscriptional gene silencing is mediated by RNA-induced silencing complexes (RISCs) that contain AGO proteins and single-stranded small RNAs. The assembly of plant AGO1-containing RISCs depends on the molecular chaperone HSP90. Here, we demonstrate that cyclophilin 40 (CYP40), protein phosphatase 5 (PP5), and several other proteins with the tetratricopeptide repeat (TPR) domain associates with AGO1 in an HSP90-dependent manner in extracts of evacuolated tobacco protoplasts (BYL). Intriguingly, CYP40, but not the other TPR proteins, could form a complex with small RNA duplex-bound AGO1. Moreover, CYP40 that was synthesized by in-vitro translation using BYL uniquely facilitated binding of small RNA duplexes to AGO1, and as a result, increased the amount of mature RISCs that could cleave target RNAs. CYP40 was not contained in mature RISCs, indicating that the association is transient. Addition of PP5 or cyclophilin-binding drug cyclosporine A prevented the association of endogenous CYP40 with HSP90-AGO1 complex and inhibited RISC assembly. These results suggest that a complex of AGO1, HSP90, CYP40, and a small RNA duplex is a key intermediate of RISC assembly in plants.
Pubmed ID: 22045333
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A clade oriented, community curated database containing genomic, genetic, phenotypic and taxonomic information for plant genomes. Genomic information is presented in a comparative format and tied to important plant model species such as Arabidopsis. SGN provides tools such as: BLAST searches, the SolCyc biochemical pathways database, a CAPS experiment designer, an intron detection tool, an advanced Alignment Analyzer, and a browser for phylogenetic trees. The SGN code and database are developed as an open source project, and is based on database schemas developed by the GMOD project and SGN-specific extensions.
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