Mutations outside of Ure2 amyloid-forming region disrupt [URE3] prion propagation

Authors

• S Kumar
• E Dine
• E Paddock
• DC Masison

Abstract

Ure2 is a regulator of nitrogen catabolism and the determinant of the yeast prion [URE3]. Its N-terminal domain can misfold to form amyloid fibers that are the basis of [URE3]. The C-terminal domain (CTD) performs the regulatory function. Amyloid-based yeast prions must replicate so their numbers keep pace with cells in expanding populations. Replication depends on fragmentation of prion fibers by Hsp104 assisted by Hsp70 and its co-chaperones, which extract monomers from the polymers causing them to break. In contrast, altering function of this machinery, or other protein quality control (PQC) factors, can eliminate prions. Moreover, endogenous activities of some PQC factors have anti-prion functions. Btn2, Cur1 and Hsp42 prevent establishment and propagation of [URE3] prions, and Hsp104 blocks establishment of [PSI+] prions. While amyloid-forming regions of several yeast prion proteins are clearly defined, our understanding of where and how factors act on prion polymers to facilitate their propagation or elimination is limited. To gain insight into these processes we identified mutations in Ure2 outside the amyloid-forming region that disrupt ability of Ure2 to propagate as [URE3], reasoning they might locate sites of interaction for chaperones or other factors rather than affecting amyloid propagation directly. Indeed, inhibition of [URE3] by some CTD mutations depended on abundance of PQC factors. Intriguingly, although all mutant proteins possess wild type amyloid-forming regions, several mutations altered the ability of Ure2 to form amyloid in vitro, which implies that disperse sites outside the amyloid-forming region are involved in interactions important for Ure2 to form amyloid.

Scientific Focus Area: Cell Biology

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