Search for SUP35 mutations that increase the spontaneous appearance of the [PSI+] prion.
Yakov Vitrenko, Susan Liebman
Dept of Genetics & Development, Columbia University College of Physicians and Surgeons, New York, NY, USA
The [PSI+] prion is an alternative, infectious conformation of Sup35, a translational termination factor. Inactivation of Sup35, either by mutation or prion formation, leads to a defect in translational termination that can be detected as nonsense suppression. The spontaneous appearance of [PSI+] is rare and is facilitated by another yeast prion, [PIN+]. We set out to find mutations in SUP35 that increase the frequency of the spontaneous appearance of [PSI+]. Such mutants would be analogous to familial PrP mutations in mammals that cause a pre-disposition to prion disease. Following expression of a pool of randomly mutagenized SUP35 in a plasmid in a [PIN+] strain we selected for mutations with the dominant nonsense suppressor phenotype characteristic of [PSI+]. Prior to this work all reported mutations of SUP35 that caused nonsense suppression were recessive. However, aside from being dominant, the suppression caused by these mutants did not appear to be due to [PSI+]: it was not infectious but was mutations contained substitutions in the GTPase domain. When the genomic wild-type SUP35 was replace with mutant alleles in [PIN+] strains, the spontaneous appearance of suppressors increased. Some of those suppressors form the wild-type strains were all [psi]. This work was supported by NIH grant GM56350.
Return to YGM 2004 Home at SGD