RNA interfering is a eukaryote-specific gene silencing by 20∼23-nucleotide (nt) microRNAs and small interfering RNAs that recruit Argonaute proteins to complementary RNAs for degradation. In humans, Argonaute2 (AGO2) has been known as the only slicer while Argonaute3 (AGO3) barely cleaves RNAs. Therefore, the intrinsic slicing activity of AGO3 remains controversial and a long-standing question. Here, we report 14-nt 3′ end-shortened variants of let-7a, miR-27a, and specific miR-17–92 families that make AGO3 an extremely competent slicer, increasing target cleavage up to ∼82-fold in some instances. These RNAs, named cleavage-inducing tiny guide RNAs (cityRNAs), conversely lower the activity of AGO2, demonstrating that AGO2 and AGO3 have different optimum guide lengths for target cleavage. Our study sheds light on the role of tiny guide RNAs.

RNA 干扰是一种真核生物特异性基因沉默，通过 20∼23 核苷酸 (nt) 的 microRNA 和小干扰 RNA 来招募 Argonaute 蛋白到互补 RNA 中进行降解。在人类中，Argonaute2 (AGO2) 被认为是唯一的切片机，而 Argonaute3 (AGO3) 几乎不能切割 RNA。因此，AGO3 的内在切片活性仍然存在争议，也是一个长期存在的问题。在这里，我们报告了 let-7a、miR-27a 和特定 miR-17-92 家族的 14-nt 3' 末端缩短变体，这些变体使 AGO3 成为一个非常有能力的切片机，在某些情况下将靶标切割提高至约 82 倍。这些RNA被称为切割诱导微小引导RNA（cityRNA），相反会降低AGO2的活性，表明AGO2和AGO3对于目标切割具有不同的最佳引导长度。我们的研究揭示了微小引导 RNA 的作用。