HHMI, Indiana University, Bloomington, IN 47405.
Department of Biology and Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN 47405.
Proc Natl Acad Sci U S A. 2021 Mar 30;118(13). doi: 10.1073/pnas.2019276118.
In plants, transcription of selfish genetic elements such as transposons and DNA viruses is suppressed by RNA-directed DNA methylation. This process is guided by 24-nt short-interfering RNAs (siRNAs) whose double-stranded precursors are synthesized by DNA-dependent NUCLEAR RNA POLYMERASE IV (Pol IV) and RNA-DEPENDENT RNA POLYMERASE 2 (RDR2). Pol IV and RDR2 coimmunoprecipitate, and their activities are tightly coupled, yet the basis for their association is unknown. Here, we show that an interval near the RDR2 active site contacts the Pol IV catalytic subunit, NRPD1, the largest of Pol IV's 12 subunits. Contacts between the catalytic regions of the two enzymes suggests that RDR2 is positioned to rapidly engage the free 3' ends of Pol IV transcripts and convert these single-stranded transcripts into double-stranded RNAs (dsRNAs).
在植物中，转座子和 DNA 病毒等自私遗传元件的转录被 RNA 指导的 DNA 甲基化所抑制。这个过程由 24 个核苷酸的短干扰 RNA（siRNA）指导，其双链前体由依赖 DNA 的核 RNA 聚合酶 IV（Pol IV）和 RNA 依赖的 RNA 聚合酶 2（RDR2）合成。Pol IV 和 RDR2 共免疫沉淀，它们的活性紧密偶联，但它们结合的基础尚不清楚。在这里，我们表明 RDR2 活性位点附近的一个间隔区与 Pol IV 的催化亚基 NRPD1 接触，NRPD1 是 Pol IV 的 12 个亚基中最大的一个。这两种酶的催化区域之间的接触表明，RDR2 被定位为能够快速与 Pol IV 转录物的游离 3' 末端结合，并将这些单链转录物转化为双链 RNA（dsRNA）。
