Mutations outside Ure2 amyloid-forming region disrupt [URE3] prion propagation, alter interactions with protein quality control factors.

The yeast prion [URE3] propagates as a misfolded amyloid form of the Ure2 protein. Propagation of amyloid-based yeast prions requires protein quality control (PQC) factors and altering PQC abundance or activity can cure cells of prions. Yeast anti-prion systems composed of PQC factors act at normal abundance to restrict establishment of the majority of prion variants that arise de novo. While these systems are well described, how they or other PQC factors interact with prion proteins remains unclear. To gain insight into such interactions we identified mutations outside the Ure2 prion-determining region that destabilize [URE3]. Despite residing in the functional domain, sixteen of seventeen mutants retained Ure2 activity. Four characterized mutations caused rapid loss of [URE3] yet allowed [URE3] to propagate under prion-selecting conditions. Two sensitized [URE3] to Btn2, Cur1 and Hsp42, but in different ways. Two others reduced amyloid formation in vitro. Of these, one impaired prion replication and the other apparently impaired transmission. Thus, widely dispersed sites outside a prion's amyloid-forming region can contribute to prion character and altering such sites can disrupt prion propagation by altering interactions with PQC factors.