Prion-Forming Ability of Ure2 of Yeasts Is Not Evolutionarily Conserved

URE3 is a prion (infectious protein) of the Saccharomyces cerevisiae Ure2p, a regulator of nitrogen catabolism. We show that wild S. paradoxus can be infected with a URE3 prion, supporting the use of S. cerevisiae as a prion test bed. We find that the Ure2p of Candida albicans and C. glabrata also regulate nitrogen catabolism. Conservation of amino acid sequence within the prion domain of Ure2p has been proposed as evidence that the URE3 prion helps its host. We show that the C. albicans Ure2p, which does not conserve this sequence, can nonetheless form a URE3 prion in S. cerevisiae, but the C. glabrata Ure2p, which does have the conserved sequence, cannot form URE3 as judged by its performance in S. cerevisiae. These results suggest that the sequence is not conserved to preserve prion forming ability.