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A transmission electron micrograph of Sup35 protein that has formed amyloid fibers from its prion structure

Though mounting evidence points to prions as the infectious element in diseases such as scrapie and Creutzfeldt-Jakob (CJD), direct proof is missing. A prion has the same amino acid sequence as the normal protein, but it has an altered structural form. The protein-only hypothesis states that a prion can cause disease and also spread it without transmitting any genetic material. Instead, it induces a change in the normal cellular protein to form the prion, which wreaks havoc in the brain. Understanding mammalian prions may be aided by studying the phenomenon in yeast, the only other organism with known prions. During the last few years several groups have used yeast to develop a clearer picture of how prions work.

Prions in Yeast

Yeast prions, unlike their mammalian counterpart, do not kill the...