title: A Tetrahymena Hsp90 co-chaperone promotes siRNA loading by ATP-dependent and ATP-independent mechanisms.
abstract: The loading of small interfering RNAs (siRNAs) and microRNAs into Argonaute proteins is enhanced by Hsp90 and ATP in diverse eukaryotes. However, whether this loading also occurs independently of Hsp90 and ATP remains unclear. We show that the Tetrahymena Hsp90 co-chaperone Coi12p promotes siRNA loading into the Argonaute protein Twi1p in both ATP-dependent and ATP-independent manners in vitro. The ATP-dependent activity requires Hsp90 and the tetratricopeptide repeat (TPR) domain of Coi12p, whereas these factors are dispensable for the ATP-independent activity. Both activities facilitate siRNA loading by counteracting the Twi1p-binding protein Giw1p, which is important to specifically sort the 26- to 32-nt siRNAs to Twi1p. Although Coi12p lacking its TPR domain does not bind to Hsp90, it can partially restore the siRNA loading and DNA elimination defects of COI12 knockout cells, suggesting that Hsp90- and ATP-independent loading of siRNA occurs in vivo and plays a physiological role in Tetrahymena.
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.
authors.forename: Sophie L
authors.initials: SL
authors.lastname: Woehrer
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.
authors.forename: Lucia
authors.initials: L
authors.lastname: Aronica
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.
authors.forename: Jan H
authors.initials: JH
authors.lastname: Suhren
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.
authors.forename: Clara Jana-Lui
authors.initials: CJ
authors.lastname: Busch
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Noto
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria kazufumi.mochizuki@imba.oeaw.ac.at.
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Mochizuki
mesh_terms: D060565:Argonaute Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D035683:MicroRNAs; D018832:Molecular Chaperones / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism*; D013768:Tetrahymena / Q000378:metabolism*
chemical_list: D060565:Argonaute Proteins; D018841:HSP90 Heat-Shock Proteins; D035683:MicroRNAs; D018832:Molecular Chaperones; D034741:RNA, Small Interfering
keywords: Argonaute protein; RISC assembly; RNAi; Tetrahymena; siRNA