RNA as a target of double-stranded RNA-mediated genetic interference in Caenorhabditis elegans

Introduction of exogenous double-stranded RNA (dsRNA) into Caenorhabditis e legans has been shown to specifically and potently disrupt the activity of genes containing homologous sequences, In this study we present evidence th at the primary interference effects of dsRNA are posttranscriptional. First , we examined the primary DNA sequence after dsRNA-mediated interference an d found no evidence for alterations. Second, we found that dsRNA-mediated i nterference with the upstream gene in a polar operon had no effect on the a ctivity of the downstream gene; this finding argues against an effect on in itiation or elongation of transcription. Third, we observed by in situ hybr idization that dsRNA-mediated interference produced a substantial, although not complete, reduction in accumulation of nascent transcripts in the nucl eus, while cytoplasmic accumulation of transcripts was virtually eliminated . These results indicate that the endogenous mRNA is the target for interfe rence and suggest a mechanism that degrades the targeted RNA before transla tion can occur. This mechanism is not dependent on the SMG system, an mRNA surveillance system in C. elegans responsible for targeting and destroying aberrant messages. We suggest a model of how dsRNA might function in a cata lytic mechanism to target homologous mRNAs for degradation.