Yota Murakami

In fission yeast, Schizosaccharomyces pombe, constitutive heterochromatin defined by methylation of histone H3 lysine 9 (H3K9me) and its binding protein Swi6/HP1 localizes at the telomere, centromere, and mating‐type loci. These loci contain DNA sequences called dg and dh , and the RNA interference (RNAi)‐dependent system establishes and maintains heterochromatin at dg/dh . Bi‐directional transcription at dg/dh induced by RNA polymerase II is critical in RNAi‐dependent heterochromatin formation because the transcribed RNAs provide substrates for siRNA synthesis and a platform for assembling RNAi factors. However, a regulator of dg/dh transcription during the establishment of heterochromatin is not known. Here, we found that a zinc‐finger protein Moc3 localizes dh and activates dh ‐forward transcription in its zinc‐finger‐dependent manner when heterochromatin structure or heterochromatin‐dependent silencing is compromised. However, Moc3 does not localize at normal heterochromatin and does not activate the dh ‐forward transcription. Notably, the loss of Moc3 caused a retarded heterochromatin establishment, showing that Moc3‐dependent dh ‐forward transcription is critical for RNAi‐dependent heterochromatin establishment. Therefore, Moc3 is a transcriptional activator that induces RNAi to establish heterochromatin.