Small double-stranded RNA (dsRNA), such as small interfering RNA (siRNA) and microRNA (miRNA), have been found to be the trigger of an evolutionary conserved mechanism known as RNA interference (RNAi). RNAi invariably leads to gene silencing via remodeling chromatin to thereby suppress transcription, degrading complementary mRNA, or blocking protein translation. Recent discoveries now suggest that dsRNAs may also act as small activating RNAs (saRNA). By targeting sequences in gene promoters, saRNAs readily induce target gene expression in a phenomenon referred to as dsRNA-induced transcriptional activation (RNAa). This discovery expands our knowledge on both the functionality and complexity small RNAs have in regulating gene expression.
Gene activation by RNAa appears to be long-lasting. Induction of gene expression has been seen to last for over ten days. The prolonged effect of RNAa could be attributed to epigenetic changes at dsRNA target sites.