RNA干扰（RNA interference，缩写为RNAi）是指一种分子生物学上由双链RNA诱发的基因沉默现象，其机制是通过阻碍特定基因的转译或转录来抑制基因表达。当细胞中导入与内源性mRNA编码区同源的双链RNA时，该mRNA发生降解而导致基因表达沉默。与其它基因沉默现象不同的是，在植物和线虫中，RNAi具有传递性，可在细胞之间传播，此现象被称作系统性RNA干扰（systemic RNAi）。在秀丽隐杆线虫上实验时还可使子一代产生基因突变，甚至于可用喂食细菌给线虫的方式让线虫得以产生RNA干扰现象。RNAi现象在生物中普遍存在。2006年，安德鲁·法厄（Andrew Z. Fire）与克雷格·梅洛（Craig C. Mello）由于在秀丽隐杆线虫的RNAi机制研究中的贡献而共同获得诺贝尔生理及医学奖。

RNAI is a non-coding RNA that is an antisense repressor of the replication of some E. coli plasmids, including ColE1. Plasmid replication is usually initiated by RNAII, which acts as a primer by binding to its template DNA. The complementary RNAI binds RNAII prohibiting it from its initiation role. The rate of degradation of RNAI is therefore a major factor in control of plasmid replication. This rate of degradation is aided by the pcnB (plasmid copy number B) gene product, which polyadenylates the 3' end of RNAI targeting it for degradation by PNPase.