Han Jiang, Kim Daniel, Morris Kevin V
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Proc Natl Acad Sci U S A. 2007 Jul 24;104(30):12422-7. doi: 10.1073/pnas.0701635104. Epub 2007 Jul 17.
siRNAs targeted to gene promoters can direct epigenetic modifications that result in transcriptional gene silencing in human cells. It is not clear whether the antisense strand of the siRNAs bind directly to DNA or to a sense-stranded RNA transcript corresponding to the known promoter region. We present evidence that an RNA polymerase II expressed mRNA containing an extended 5' untranslated region that overlaps the gene promoter is required for RNA-directed epigenetic modifications and transcriptional silencing of the RNA-targeted promoter. These promoter-associated RNAs were detected by their hybridization to the antisense strand of the complementary promoter-directed siRNA. Antisense phosphorothioate oligodeoxynucleotides were used to degrade the promoter-associated RNA transcripts, the loss of which abrogated the effect of siRNA-mediated transcriptional gene silencing, as well as the complexing of the siRNA with the silent state histone methyl mark and the promoter-associated RNA. These data demonstrate that low-copy promoter-associated RNAs transcribed through RNAPII promoters are recognized by the antisense strand of the siRNA and function as a recognition motif to direct epigenetic silencing complexes to the corresponding targeted promoters to mediate transcriptional silencing in human cells.
靶向基因启动子的小干扰RNA（siRNAs）可引导表观遗传修饰，从而导致人类细胞中的转录基因沉默。目前尚不清楚siRNAs的反义链是直接与DNA结合，还是与对应已知启动子区域的有义链RNA转录本结合。我们提供的证据表明，对于RNA引导的表观遗传修饰以及RNA靶向启动子的转录沉默而言，一种含有与基因启动子重叠的延长5'非翻译区的RNA聚合酶II表达的mRNA是必需的。这些启动子相关RNA通过与互补启动子导向的siRNA的反义链杂交而被检测到。反义硫代磷酸酯寡脱氧核苷酸被用于降解启动子相关的RNA转录本，其缺失消除了siRNA介导的转录基因沉默的效果，以及siRNA与沉默状态组蛋白甲基化标记和启动子相关RNA的复合。这些数据表明，通过RNA聚合酶II启动子转录的低拷贝启动子相关RNA被siRNA的反义链识别，并作为一种识别基序，将表观遗传沉默复合物导向相应的靶向启动子，以介导人类细胞中的转录沉默。
