Prion-Dependent Lethality of sup35 Missense Mutations Is Caused by Low GTPase Activity of the Mutant eRF3 Protein

TL;DR

This paper shows that certain missense mutations in the yeast Sup35 protein cause cell death when a prion is present due to reduced protein activity.

Contribution

The study identifies that missense mutations in the GTPase region of Sup35 lead to prion-dependent lethality through reduced translation termination activity.

Findings

sup35 missense mutations in the GTPase region cause [PSI+] prion-dependent lethality due to low eRF3 activity.

Mutant Sup35 proteins retain prion aggregation ability but fail to maintain cell viability.

The mutations D363N, R372K, and T378I reduce GTPase activity of the Sup35 protein.

Abstract

The essential SUP35 gene encodes yeast translation termination factor Sup35/eRF3. The N-terminal domain of Sup35 is also responsible for Sup35 prionization that leads to generation of the [PSI+] prion. Previously we isolated different types of sup35 mutations (missense and nonsense) and demonstrated that sup35 nonsense mutations (sup35-n) are incompatible with the [PSI+] prion, leading to lethality of sup35-n [PSI+] haploid cells. Here, we show that sup35 missense mutations (sup35-m) within conservative regions of the Sup35 C-domain result in lethality of [PSI+] cells because of weak activity of Sup35/eRF3 as a translation termination factor. Mutant Sup35 maintain their ability to be incorporated into pre-existing [PSI+] aggregates and to form amyloid aggregates in vitro, while sup35-m mutations do not influence the [PSI+] prion induction and stability. All these mutations (D363N, R372K, T378I) are located in the conservative GTPase region of Sup35, decreasing the GTPase activity of mutated proteins. We propose that such low activity of mutant Sup35 combined with aggregation of Sup35 constituting the [PSI+] prion is not sufficient to maintain the viability of yeast cells.

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