Prion-like determinant [NSI+] decreases the expression of the SUP45 gene in Saccharomyces cerevisiae

Previously, we described and characterized the yeast nonchromosomal determinant [NSI+], which possesses prion properties. This determinant causes a decrease in fidelity of translation termination, which is phenotypically detectable as the nonsense suppression in the strains with decreased functional activity of eRF3 release factor. As a result of the genetic screen, we demonstrated that an increase in the expression of SUP45 that encodes the eRF1 release factor (Sup45), masks, but does not eliminate nonsense suppression in the [NSI+] strains. In the present study, we first demonstrated the direct cause for the nonsense suppression in [NSI+] strains. We demonstrated that [NSI+] decreases the relative amounts of SUP45 mRNA, which causes a decrease in the amounts of Sup45 protein that can be detected in the stationary growth phase. The data obtained suggest the structural protein of [NSI+] seems to be either a transcription factor or participates in the regulation of cellular mRNA stability.