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]
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. Abstract and author contributions: active-site mutations, functional assays and experimental roles
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.
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