Schematic representation of constitutive heterochromatin formation in fission yeast. Sir2 is responsible for deacetylation of histone tails. Clr4 methylates histone H3 on lysine 9 (H3K9me3), which is an anchor for the HP1 homolog Swi6. RNA Polymerase II (RNAPII) transcribes pericentromeric noncoding repeats in single strand RNA. Rdp1, a component of the RNA-dependent RNA polymerase, can generate a double-strand RNA, which is digested by Dicer to produce short interfering RNAs (siRNAs). The siRNAs associate with the RITS (RNA-induced initiation of transcriptional silencing) complex, which is responsible for further recruitment of Clr4, and therefore stimulates further H3K9me3 and maintains local heterochromatin.