TY - JOUR T1 - Catalytic properties of RNA polymerases IV and V: accuracy, nucleotide incorporation and rNTP/dNTP discrimination JF - bioRxiv DO - 10.1101/117184 SP - 117184 AU - Michelle Marasco AU - Weiyi Li AU - Michael Lynch AU - Craig S. Pikaard Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/03/15/117184.abstract N2 - Catalytic subunits of DNA-dependent RNA polymerases of bacteria, archaea and eukaryotes share hundreds of ultra-conserved amino acids. Remarkably, the plant-specific RNA silencing enzymes, Pol IV and Pol V differ from Pols I, II and III at ~140 of these positions, yet remain capable of RNA synthesis. Whether these amino acid changes in Pols IV and V alter their catalytic properties in comparison to Pol II, from which they evolved, is unknown. Here, we show that Pols IV and V differ from one another, and Pol II, in nucleotide incorporation rate, transcriptional accuracy and the ability to discriminate between ribonucleotides and deoxyribonucleotides. Pol IV transcription is notably error-prone, which may be tolerable, or even beneficial, for biosynthesis of siRNAs targeting transposon families in trans. By contrast, Pol V exhibits high fidelity transcription, suggesting a need for Pol V transcripts to faithfully reflect the DNA sequence of target loci in order to recruit siRNA-Argonaute protein silencing complexes. ER -