2．启动子区 RNAi 技术
M. F. Mett等证明含有启动子区的dsRNA在植物体内同样被切割成 21-23核苷酸长的片段，这种 dsRNA可使内源性相应的DNA序列甲基化，从而使启动子失去功能，使其下游基因沉默。
由于多基因家族的各成员之间具有高度的同源性，因而使用编码区 RNAi 技术很难将各个成员区分开来研究，而多基因家族内的启动子序列通常比编码区变化大，因此若采用启动子区 RNAi 技术，则有希望将多基因家族的各个成员区分开来研究。这样综合编码区 RNAi 技术和启动子区 RNAi 技术的信息即可更全面地了解多基因家族地各成员的功能。
RNAi现象存在的广泛性远远超过人们的预期，对此问题的深入研究结果将为进化的观点提供有力左证。而与其它几种进行功能丧失或降低突变的技术相比，RNAi 技术具有明显的优点，它比反义RNA技术和同源共抑制更有效，更容易产生功能丧失或降低突变。而且通过与细胞特异性启动子及可诱导系统的结合使用，可以在发育的不同时期或不同器官中有选择地进行，再与 T-DNA技术造成的功能永久性缺失相比较，则这个RNAi 的实验技术则是更受科学家所偏爱的。由于科学家们的努力工作，一个崭新的RNA时代呼之欲出。
RNA interference (RNAi) refers to the post-transcriptional silencing of gene expression due to the presence of double stranded RNA (dsRNA). This phenomenon was first described in plants in the early 1990’s when it was discovered that the introduction of an extra copy of an endogenous gene led to the degradation of both the introduced and endogenous gene transcripts (Vaucheret et. al., Post-transcriptional gene silencing in plants, J.Cell Science, 2001 Sep; 114 (pt 17):3083-91). In plants, this peculiar behavior was called “co-suppression”. Soon, similar findings were seen in the fungus Neurospora crassa, where it was termed “quelling”. In 1998, Fire et. al., demonstrated that the introduction of dsRNA into the nematode Caenorhabditis elegans interfered with gene expression in a sequence specific manner (Fire et. al., Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans, Nature, 1998 Feb 19; 391(6669):806-11). The term for this phenomenon became “RNA interference” or “RNAi”.
