A new prion controls fungal cell fusion incompatibility

In solving a genetic puzzle posed by George Rizet in 1952 (1), Coustou, Deleu, Saupe, and Begueret report (2) evidence for the first prion (infectious protein) that carries out a normal function. It was studies of scrapie that gave rise to the prion concept, namely, that a normal cellular protein could change to an abnormal form (the prion form) that may be unable to carry out its normal function, but has acquired the ability to convert its normal form into this same abnormal (prion) form. This altered protein, by catalyzing, not its own synthesis, but its own alteration, becomes an infectious agent (a prion) if it can get from cell to cell or from individual to individual (reviewed in refs. 3–6).