Analysis of Small Critical Regions of Swi1 Conferring Prion Formation, Maintenance, and Transmission

Abstract

contains several prion elements, which are epigenetically transmitted as self-perpetuating protein conformations. One such prion is [ ], whose protein determinant is Swi1, a subunit of the SWI/SNF chromatin-remodeling complex. We previously reported that [ ] formation results in a partial loss-of-function phenotype of poor growth in nonglucose medium and abolishment of multicellular features. We also showed that the first 38 amino acids of Swi1 propagated []. We show here that a region as small as the first 32 amino acids of Swi1 (Swi1) can decorate [] aggregation and stably maintain and transmit [] independently of full-length Swi1. Regions smaller than Swi1 are either incapable of aggregation or unstably propagate []. When fused to Sup35MC, the [ ] determinant lacking its PrD, Swi1 and Swi1 can act as transferable ionomains (PrDs). The resulting fusions give rise to a novel chimeric prion, [], exhibiting []-like nonsense suppression. Thus, an NH-terminal region of ∼30 amino acids of Swi1 contains all the necessary information for prion formation, maintenance, and transmission. This PrD is unique in size and composition: glutamine free, asparagine rich, and the smallest defined to date. Our findings broaden our understanding of what features allow a protein region to serve as a PrD.

A brief overview of the Swi1 prion—[SWI+]

“…The identification of [SWI + ] and Swi1 as its prion determinant in yeast was the first identification of a global transcriptional regulator being able to form a prion (Du et al 2008). A small, asparagine-rich extreme amino-terminal region has been described as the major determinant of [SWI + ], and the ability of this region to propagate and maintain [SWI + ] is notable (Crow, Du and Li 2011;Valtierra, Du and Li 2017). [SWI + ] has also displayed important and varied interplay with other yeast prions including [PSI + ] and [RNQ + ]-developing the knowledge regarding prion-prion interactions and formation of prions (Du and Li 2014;Nizhnikov et al 2016;Du et al 2017).…”

“…This capability was demonstrated via the classic Sup35 assay (Sondheimer and Lindquist 2000). In this assay, Swi1 1-38 , Swi1 1-32 and Sw1 1-31 all could recapitulate the [PSI + ]like phenotype as artificial prions ([SPS + ]) when fused with the MC region of Sup35 (Valtierra, Du and Li 2017). Further work is necessary to determine the roles of the extreme amino-terminal region (∼30 amino acids) in Swi1 prion de novo formation and propagation regarding the prion-forming frequency, stabilization and interactions with other proteins.…”

“…Upon further inspection, smaller amino-terminal regions (down to, and including Swi1 1-32 ) were found to be able to coaggregate with full-length Swi1 in [SWI + ] cells, maintain the prion fold in the absence of the full-length protein and transmit the prion conformation back to full-length Swi1 (Valtierra, Du and Li 2017). In addition, when full-length Swi1 was overexpressed, other smaller truncations (down to, and including Swi1 1-28 ) aggregated in [SWI + ] cells-although these smaller constructs could not stably maintain [SWI + ] as the prion would be quickly lost upon passaging.…”

Identifying Endogenous Cellular Proteins Destabilizing the Propagation of Swi1 Prion upon Overproduction

“…We have previously shown that the N-region contains the prion domain (PrD) that is essential and sufficient for [ SWI + ] formation and propagation [ 20 , 21 ]. Intriguingly, a region that contains the first 32–38 amino acids of Swi1 is largely asparagine-rich, can join [ SWI + ] aggregates, propagate the [ SWI + ] conformation, and act as a transferable PrD [ 22 , 23 , 24 ]. [ SWI + ] relies on chaperones for its propagation and is highly sensitive to alterations in the Hsp70 chaperone system activity [ 14 , 25 ].…”

Elucidating the regulatory mechanism of Swi1 prion in global transcription and stress responses

“…Its amino-terminal region enriched in asparagine is dispensable for the remodeling function and contains an amyloid core domain that can form amyloid in vitro 27 , 28 . Swi1 harbors a prion domain (PrD) at its N-terminus and the first 30 or so residues is sufficient to support the prion propagation 29 , 30 . The C-terminal region is not involved in the prion formation or transmission but is essential for normal function of Swi1 27 , 31 .…”