DamID for Swi6, Rdp1 and Dcr1 in Schizosaccharomyces pombe

In the fission yeast Schizosaccharomyces pombe, the RNA interference (RNAi) pathway is required to generate small interfering RNAs (siRNAs) that mediate heterochromatic silencing of centromeric repeats. Here we demonstrate that RNAi also functions to repress genomic elements other than constitutive heterochromatin. Using DamID (DNA adenine methyltransferase identification) we show that Dcr1 and Rdp1 physically associate with some euchromatic genes, non-coding RNA (ncRNA) genes, and retrotransposon long terminal repeats (LTRs), and that this association is independent of the Clr4 histone methyltransferase. Physical association of RNAi with chromatin is sufficient to trigger a silencing response but not to assemble heterochromatin. The mode of silencing at the newly identified RNAi targets is consistent with a co-transcriptional gene silencing model as proposed earlier and functions with trace amounts of siRNAs. We anticipate that similar mechanisms could also be operational in other eukaryotes. Methylation levels in strains expressing Dam-Swi6, Dam-Rdp1 and Dam-Dcr1 were compared to those in a Dam only expressing strain. Three biological replicates for each experiment were performed.