Mad Cow Disease or BSE (bovine spongiform encephalopathy) is a progressive neurological disorder of cattle that results from infection by an unusual transmissible agent called a prion. The nature of the transmissible agent is not well understood. Currently, the most accepted theory is that the agent is a modified form of a normal protein known as prion protein. For reasons that are not yet understood, the normal prion protein changes into a pathogenic (harmful) form that then damages the central nervous system of cattle.
The culprit behind mad cow disease, a.k.a. bovine spongiform encephalopathy, is the most infamous mammalian form of prions. Prions are misfolded proteins that are capable of growing, replicating, and being passed on to daughter cells, that is, they are by themselves heritable. Beyond their disease manifestation, prions also occur naturally in some organisms (such as yeast) and may play important roles in their growth and development. Now, Osherovich and colleagues have identified the amino acid sequences that allow prions to aggregate and replicate, and thereby pass through generations of cells - and prove this by designing an artificial yeast prion that does not exist in nature.