Fig. 1. Model for post-transcriptional gene silencing in Neurospora. dsRNA can be produced either directly from inverted repeats or indirectly whereby an RdRP (QDE1) makes a complementary strand of an aberrant single-stranded (ss)RNA produced from the transgene. The aberrant RNA is a result of an epigenetic modification of the transgenic locus driven by the repetitive nature of the transgene and mediated by QDE3. Before Dicer processes the dsRNA into the siRNAs, the dsRNA is used as a template by RdRP (QDE1) to synthesize a diffusible factor. The siRNAs are subsequently transferred by QDE2 from Dicer to the mRNA-degrading enzyme. See text for additional details.