Distinct Subregions of Swi1 Manifest Striking Differences in Prion Transmission and SWI/SNF Function

Abstract

We have recently reported that the yeast chromatin-remodeling factor Swi1 can exist as a prion, [SWI⁺], demonstrating a link between prionogenesis and global transcriptional regulation. To shed light on how the Swi1 conformational switch influences Swi1 function and to define the sequence and structural requirements for [SWI⁺] formation and propagation, we functionally dissected the Swi1 molecule. We show here that the [SWI⁺] prion features are solely attributable to the first 327 amino acid residues (N), a region that is asparagine rich. N was aggregated in [SWI⁺] cells but diffuse in [swi⁻] cells; chromosomal deletion of the N-coding region resulted in [SWI⁺] loss, and recombinant N peptide was able to form infectious amyloid fibers in vitro, enabling [SWI⁺] de novo formation through a simple transformation. Although the glutamine-rich middle region (Q) was not sufficient to aggregate in [SWI⁺] cells or essential for SWI/SNF function, it significantly modified the Swi1 aggregation pattern and Swi1 function. We also show that excessive Swi1 incurred Li⁺/Na⁺ sensitivity and that the N/Q regions are important for this gain of sensitivity. Taken together, our results provide the final proof of “protein-only” transmission of [SWI⁺] and demonstrate that the widely distributed “dispensable” glutamine/asparagine-rich regions/motifs might have important and divergent biological functions.

We thank Gyoung-Eun Kim for technical assistance and Yimei Chen, University of Chicago, for helping with electron microscopy imaging.

This work was supported by a grant from the U.S. National Institutes of Health (R01NS056086) to L.L.