Background Proteins are chains of chemicals called amino acids linked together like beads on a string. The prion protein has about 250 amino acids. The amino acid string does not remain linear once it is made, however, and the properties of the different amino acids make the protein fold into a specific shape or conformation. The conformation of a protein determines its function. Different amino acid sequences produce proteins with different conformations and functions.
Genes determine the sequence of amino acids in a protein.
First, infectious prions isolated from brain tissue contain PrPSc. A process called purification removes molecules that are not part of the prion. The purity of a prion preparation is judged by how much infectivity is present for each gram of protein or nucleic acid. PrPSc is the only protein found in the best-purified preparations. Thus, the only molecule identified in the infectious particle is PrPSc.