Abstract
The concept of "protein-based inheritance" defines prions as epigenetic determinants that cause several heritable traits in eukaryotic microorganisms, such as Saccharomyces cerevisiae and Podospora anserina. Previously, we discovered a non-chromosomal factor, [NSI+], which possesses the main features of yeast prions, including cytoplasmic infectivity, reversible curability, dominance, and non-Mendelian inheritance in meiosis. This factor causes omnipotent suppression of nonsense mutations in strains of S. cerevisiae bearing a deleted or modified Sup35 N-terminal domain. In this work, we identified protein determinants of [NSI+] using an original method of proteomic screening for prions. The suppression of nonsense mutations in [NSI+] strains is determined by the interaction between [SWI+] and [PIN+] prions. Using genetic and biochemical methods, we showed that [SWI+] is the key determinant of this nonsense suppression, whereas [PIN+] does not cause nonsense suppression by itself but strongly enhances the effect of [SWI+]. We demonstrated that interaction of [SWI+] and [PIN+] causes inactivation of SUP45 gene that leads to nonsense suppression. Our data show that prion interactions may cause heritable traits in Saccharomyces cerevisiae.
Highlights
Prions are proteins that convert between structurally distinct states, of which one or more is transmissible [1]
Since we proposed that weak nonsense suppression in the [NSI+] rnqΔ strain was caused by an unknown prion that was undetectable by the standard Proteomic screening and identification of amyloids (PSIA) approach, we modified the PSIA
We demonstrated that Swi1-yellow fluorescent protein (YFP) and Rnq1-cyan fluorescent protein (CFP) proteins do not colocalize in the D938 [SWI+][PIN+] strain (Fig 5C)
Summary
Prions are proteins that convert between structurally distinct states, of which one or more is transmissible [1]. We developed the proteomic method for identification of yeast prion proteins that form amyloid-like aggregates resistant to treatment with ionic detergents [22] Using this method we demonstrated that the nonsense suppression in the [NSI+] strain is a result of interaction between [PIN+] and. Prion inactivation of Swi protein causes weak nonsense suppression, [PIN+] enhances this effect, whereas deletion of SWI1 leads to strongest nonsense suppressor phenotype To reproduce these results, the strains with different combination of prions (26-1-4-1-1-D931 [swi-][PIN+], 12-1-4-1-1-D931 [SWI+][pin-], and 161-4-1-1-D931 [SWI+][PIN+]) were obtained by transformation of [swi-][pin-] cells with protein lysates (see “Materials and Methods”). Interaction between [SWI+] and [PIN+] causes decreased SUP45 expression and leads to nonsense suppression
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