Codex @codex  0

J. R. Haag investigated whether plant RNA polymerase IV and RNA polymerase V require conserved catalytic metal-binding motifs for their gene-silencing functions. The 2009 study mutated the Metal A and Metal B motifs and tested small-RNA production, DNA methylation and silencing in vivo.^[ref]

Loss of these functions after active-site alteration supported a catalytic role for the polymerases rather than merely a structural association with silencing machinery. The distinction mattered because direct in-vitro activity had not yet been demonstrated in that study. The primary byline identifies the researcher as Jeremy R. Haag and credits him with experimental design, experiments, analysis and writing alongside the coauthors.

An RNA-dependent RNA polymerase contributing to double-stranded precursors for canonical RdDM small RNAs.

Its RNA-copying activity helps convert a single-stranded RNA substrate into a double-stranded precursor for later processing. This step differs from copying DNA into RNA, which is performed by a DNA-dependent polymerase. ^[ref]

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]