Cap1 2′-O-ribose methyltransferase (CMTR1) modifies RNA transcripts containing the 7-methylguanosine cap via 2′-O-ribose methylation of the first transcribed nucleotide, yielding cap1 structures. However, the role of CMTR1 in small RNA-mediated gene silencing remains unknown. Here, we identified and characterized a Drosophila CMTR1 gene (dCMTR1) mutation. We found that the catalytic activity of dCMTR1 was involved in the biogenesis of small interfering RNAs (siRNAs) but not microRNAs. Additionally, dCMTR1 interacted with R2D2, a key component for the assembly of the RNA-induced silencing complex (RISC) containing Argonaute 2 (Ago2). Consistent with this finding, loss of dCMTR1 function impaired RISC assembly by inhibiting the unwinding of Ago2-bound siRNA duplexes, thus preventing the retention of the guide strand. Moreover, dCMTR1 is unlikely to modify siRNAs during RISC assembly. Collectively, our data indicate that dCMTR1 is a positive regulator of the small RNA pathway associated with Ago2 with roles in both siRNA biogenesis and RISC assembly.

Cap1 2'- O-核糖甲基转移酶（CMTR1）通过第一个转录核苷酸的2'- O-核糖甲基化修饰含有7-甲基鸟苷帽的RNA转录物，产生cap1结构。但是，CMTR1在小RNA介导的基因沉默中的作用仍然未知。在这里，我们鉴定并鉴定了果蝇CMTR1基因（dCMTR1）突变。我们发现dCMTR1的催化活性与小干扰RNA（siRNA）的生物发生有关，而与microRNA无关。此外，dCMTR1与R2D2相互作用，R2D2是组装含Argonaute 2（Ago2）的RNA诱导的沉默复合物（RISC）的关键组件。与此发现一致，dCMTR1功能的丧失通过抑制与Ago2结合的siRNA双链体的解链而损害了RISC装配，从而阻止了导链的保留。此外，dCMTR1不太可能在RISC组装过程中修饰siRNA。总体而言，我们的数据表明dCMTR1是与Ago2相关的小RNA途径的正调节剂，在siRNA生物发生和RISC组装中均起作用。