 The mechanism by which the RITS complex induces heterochromatin formation and organization is not well understood . Most studies have focused on the mating @-@ type region in fission yeast , which may not be representative of activities in other genomic regions / organisms . In maintenance of existing heterochromatin regions , RITS forms a complex with siRNAs complementary to the local genes and stably binds local methylated histones , acting co @-@ transcriptionally to degrade any nascent pre @-@ mRNA transcripts that are initiated by RNA polymerase . The formation of such a heterochromatin region , though not its maintenance , is dicer @-@ dependent , presumably because dicer is required to generate the initial complement of siRNAs that target subsequent transcripts . <unk> maintenance has been suggested to function as a self @-@ reinforcing feedback loop , as new siRNAs are formed from the occasional nascent transcripts by RdRP for incorporation into local RITS complexes . The relevance of observations from fission yeast mating @-@ type regions and centromeres to mammals is not clear , as heterochromatin maintenance in mammalian cells may be independent of the components of the RNAi pathway . 
