Heat Shock Molecular Chaperone Hsp90 Is Involved In Heterochromatin Assembly By Stabilizing Multiple Gene Silencing Complexes In Fission Yeast

Eukaryotic genomic DNA is fold with histones and non-histone proteins in the form of chromatin,which is classified into euchromatin and heterochromatin.Heterochromatin,histone H3K9-methylated.plays important roles in gene silencing,development and genome stability.In the fission yeast,Schizosaccharomyces pombe,the RNA interfering(RNAi)is required for heterochromatin assembly.Therefore,Hsp90 may contribute to heterochromatin assembly in fission yeast.Recent studies in higher enkaryotes had revealed that Hsp90,a essential and ubiquitous molecular chaperone with key roles in the folding,activation and assembly of client proteins,facilitates the loading of small RNAs into Argonaute protein in vitro.Here,we examined the potential in vivo function of fission yeast Hsp90 encoded by Swo1+ in heterochromatic gene silencing.We found that the heterochromatic gene silencing at pericentromeres,rDNA regions and mating-type locus was alleviated in swo1-26 mutant.Then we observed that specifically abolishing Hsp90 from centromeres resulted in strong disruption of heterochromatic silencing.Furthermore,the swo1-26 mutation drastically disrupted the formation and stabilization of the RNAi effector complexes RITS and ARC.We also showed that fission yeast Hsp90 physically interacted with Ago1 and Tas3.Interstingly,we further show that swo1-26 mutation also disrupted the formation and stabilization of SHREC.Finally,we observed that swo1-26 mutation dramatically relie-ved gene silencing at minichromosome subtelometre.Furthermore,the protein level of Poz1,a component of Shelterin complex faciliating heterochromatin assembly at subtelomere,was reduced in swo1-26 mutation cells.However,Shelterin assembly has no defect in swo1-26 mutation cells.Interstingly,we further show that recruiting CLRC and SHREC by Shelterin was disrupted in swo1-26 mutation cells.Thus,our data provided evidence that fission yeast Hsp90 is involved in heterochomatin assembly and gene silencing through stabilizing multiple gene silencing effector complexes,which contributes to our understanding of Hsp90 in heterochromatin assembly.