The use of RNA-dependent RNA polymerase plays a major role in RNA interference in eukaryotes, a process used to silence gene expression via small interfering RNAs (siRNAs) binding to mRNA rendering them inactive. Eukaryotic  RdRp becomes active in the presence of dsRNA, and is a less widely distributed compared to other RNAi components as it lost in some animals, though still found in C. elegans and P. tetraurelia and plants. This presence of dsRNA triggers the activation of  RdRp and RNAi processes by priming the initiation of RNA transcription through the introduction of siRNAs into the system. In C. elegans, siRNAs are integrated into the RNA-induced silencing complex, RISC, which works alongside mRNAs targeted for interference to recruit more  RdRps to synthesize more secondary siRNAs and repress gene expression.