Marasco Michelle, Li Weiyi, Lynch Michael, Pikaard Craig S
Department of Biology, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA.
Department of Molecular and Cellular Biochemistry, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA.
Nucleic Acids Res. 2017 Nov 2;45(19):11315-11326. doi: 10.1093/nar/gkx794.
All eukaryotes have three essential nuclear multisubunit RNA polymerases, abbreviated as Pol I, Pol II and Pol III. Plants are remarkable in having two additional multisubunit RNA polymerases, Pol IV and Pol V, which synthesize noncoding RNAs that coordinate RNA-directed DNA methylation for silencing of transposons and a subset of genes. Based on their subunit compositions, Pols IV and V clearly evolved as specialized forms of Pol II, but their catalytic properties remain undefined. 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 considerably more error-prone than Pols II or V, which may be tolerable in its synthesis of short RNAs that serve as precursors for siRNAs targeting non-identical members of transposon families. By contrast, Pol V exhibits high fidelity transcription, similar to Pol II, suggesting a need for Pol V transcripts to faithfully reflect the DNA sequence of target loci to which siRNA-Argonaute silencing complexes are recruited.
所有真核生物都有三种重要的核多亚基RNA聚合酶，简称为Pol I、Pol II和Pol III。植物的特别之处在于还有另外两种多亚基RNA聚合酶，即Pol IV和Pol V，它们合成非编码RNA，这些非编码RNA协调RNA指导的DNA甲基化，从而使转座子和一部分基因沉默。基于它们的亚基组成，Pol IV和Pol V显然是作为Pol II的特殊形式进化而来的，但它们的催化特性仍不明确。在这里，我们表明Pol IV和Pol V在核苷酸掺入率、转录准确性以及区分核糖核苷酸和脱氧核糖核苷酸的能力方面彼此不同，也与Pol II不同。Pol IV转录比Pol II或Pol V更容易出错，这在其合成作为靶向转座子家族不同成员的小干扰RNA（siRNA）前体的短RNA时可能是可以容忍的。相比之下，Pol V表现出与Pol II相似的高保真转录，这表明需要Pol V转录本忠实地反映招募了siRNA-AGO沉默复合体的靶位点的DNA序列。
