In the fission yeast Schizosaccharomyces pombe, both RNAi machinery and RNAi-independent factors mediate transcriptional and posttranscriptional silencing and heterochromatin formation. Here, we show that the silencing of reporter genes at major native heterochromatic loci (centromeres, telomeres, mating-type locus and rDNA regions) and an artificially induced heterochromatin locus is alleviated in a fission yeast hsp90 mutant, hsp90-G84C. Also, H3K9me2 enrichment at heterochromatin regions, especially at the mating-type locus and subtelomeres, is compromised, suggesting heterochromatin assembly defects. We further discovered that Hsp90 is required for stabilization or assembly of the RNA-induced transcriptional silencing (RITS) and Argonaute siRNA chaperone (ARC) RNAi effector complexes, the RNAi-independent factor Fft3, the shelterin complex subunit Poz1 and the Snf2/HDAC-containing repressor complex (SHREC). Our ChIP data suggest that Hsp90 regulates the efficient recruitment of the methyltransferase/ubiquitin ligase complex CLRC by shelterin to chromosome ends and targeting of the SHREC and Fft3 to mating type locus and/or rDNA region. Finally, our genetic analyses demonstrated that increased heterochromatin spreading restores silencing at subtelomeres in the hsp90-G84C mutant. Thus, this work uncovers a conserved factor critical for promoting RNAi-dependent and -independent heterochromatin assembly and gene silencing through stabilizing multiple effectors and effector complexes.

在裂殖酵母粟酒裂殖酵母中，RNAi 机制和 RNAi 独立因子均介导转录和转录后沉默以及异染色质形成。在这里，我们表明，在裂殖酵母 hsp90 突变体 hsp90-G84C 中，主要天然异染色质位点（着丝粒、端粒、交配型位点和 rDNA 区域）和人工诱导的异染色质位点的报告基因沉默得到缓解。此外，H3K9me2 在异染色质区域的富集，特别是在交配型基因座和亚端粒处，受到损害，表明异染色质组装缺陷。我们进一步发现 Hsp90 是 RNA 诱导转录沉默 (RITS) 和 Argonaute siRNA 伴侣 (ARC) RNAi 效应复合物、RNAi 独立因子 Fft3、shelterin 复合物亚基 Poz1 和 Snf2/HDAC- 的稳定或组装所必需的。含有阻遏物复合物（SHREC）。我们的 ChIP 数据表明，Hsp90 通过将 SHREC 和 Fft3 靶向至交配型基因座和/或 rDNA 区域，调节甲基转移酶/泛素连接酶复合物 CLRC 的有效招募。最后，我们的遗传分析表明，增加的异染色质扩散可以恢复hsp90-G84C突变体亚端粒的沉默。因此，这项工作通过稳定多个效应子和效应子复合物，揭示了一个对于促进依赖于RNAi和不依赖于RNAi的异染色质组装和基因沉默至关重要的保守因子。