RNA polymerase IV is a specialized plant nuclear RNA polymerase required for major small-RNA-dependent silencing pathways. Its transcripts are used with an RNA-dependent polymerase to generate precursors of small interfering RNAs. These help guide RNA-directed DNA methylation, while RNA polymerase V contributes a distinct scaffold-transcript function. Mutating conserved catalytic motifs disrupts silencing, supporting a requirement for polymerase activity rather than only structural presence. [ref]
Metal A and metal B sites of nuclear RNA polymerases Pol IV and Pol V are required for siRNA-dependent DNA methylation and gene silencing by J. R. Haag and others. Haag and others, 2009, catalytic metal-site mutations and siRNA-dependent silencing
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