Yeast cells manufacture a protein called Sup35, which displays prion-like behaviour: it forms aggregates and converts its normal counterpart to the prion version. Previous work by Peter Chien and Jonathan Weissman of the University of California, San Francisco, showed that a species barrier prevents the prion version of Sup35 in one yeast species from converting Sup35 of a different yeast species into the prion version, and vice versa (Cell 2000, 100:277-288).

In a study published in 8 March Nature, Chien and Weissman engineered a chimaeric prion that combined Sup35 segments from two yeast species — Saccharomyces cerevisiae and Candida albicans. When introduced into each species of yeast, the chimaera could adopt the shape of the prion specific for that species (Nature 2001, 410:223-227).

The results suggest that a single protein — in this case Sup35 — can adopt many prion conformations, some of...