The yeast prion [URE3] can be greatly induced by a functional mutated URE2allele

The non-Mendelian element [URE3] of yeast is considered to be a prion form of the Ure2 protein. The [URE3] phenotype occurs at a frequency of 10(-5) i n haploid yeast strains, is reversible, and its frequency is increased by o verexpressing the URE2 gene. We created a new mutant of the Ure2 protein, c alled H2p, which results in a 1000-fold increase in the rate of [URE3] occu rrence. To date, only the overexpression of various C-terminal truncated mu tants of Ure2p gives rise to a comparable level. The h2 allele is, thus, th e first characterized URE2 allele that induces prion formation when express ed at a low level. By shuffling mutated and wild-type domains of URE2, we a lso created the first mutant Ure2 protein that is functional and induces pr ion formation, We demonstrate that the domains of URE2 function synergistic ally in cis to induce [URE3] formation, which highlights the importance of intramolecular interactions in Ure2p folding. Additionally, we show using a green fluorescent protein (GFP) fusion protein that the h2 allele exhibits numerous filiform structures that are not generated by the wild-type prote in.