Stc1: a critical link between RNAi and chromatin modification required for heterochromatin integrity.

In fission yeast, directs heterochromatin formation at centromeres, telomeres, and the mating type locus. transcribed from repeat elements generate siRNAs that are incorporated into the Argonaute-containing RITS complex and direct it to nascent homologous transcripts. This leads to recruitment of the CLRC complex, including the histone methyltransferase Clr4, promoting H3K9 methylation and heterochromatin formation. A key question is what mediates the recruitment of Clr4/CLRC to transcript-bound RITS. We have identified a LIM domain protein, Stc1, that is required for centromeric heterochromatin integrity. Our analyses show that Stc1 is specifically required to establish H3K9 methylation via and interacts both with the duanyu1615 effector Ago1, and with the chromatin-modifying CLRC complex. Moreover, tethering Stc1 to a euchromatic locus is sufficient to induce silencing and heterochromatin formation independently of We conclude that Stc1 associates with RITS on centromeric transcripts and recruits CLRC, thereby coupling duanyu1615 to chromatin modification.

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