SCIENCEThe Real Reason Prion Diseases Spread Without DNA8 min read

The Radiation Experiment That Rewrote Assumptions

A pivotal clue came from a radiobiologist named Tikvah Alper, who conducted a series of experiments on scrapie-infected tissue in the 1960s. Her team exposed the tissue to ultraviolet radiation, which is known to damage and degrade DNA and RNA — the nucleic acids that viruses and bacteria rely on for replication. Standard infectious agents lose their ability to transmit disease under this treatment. Scrapie-infected tissue did not. Even after irradiation intense enough to destroy any nucleic acid present, the tissue remained capable of transmitting the disease. This finding raised an uncomfortable question that the slow-virus model could not answer: if the infectious agent had no DNA or RNA, what exactly was it? Alper’s data suggested the answer might be a protein, but that idea contradicted decades of established biology.

Why Prusiner Switched to Hamsters

When Prusiner began his investigation in earnest, he initially worked with mice, studying how scrapie infected their spleens and brains. The problem was time: mice took one to two years to develop visible symptoms of the disease, making experiments slow and expensive. He switched to hamsters after discovering they developed symptoms within roughly 70 days of infection — a much more workable timeline for systematic research. Using hamster tissue, Prusiner’s team could run multiple rounds of experiments, systematically exposing infected samples to different chemical and physical treatments to determine which ones disrupted transmission and which did not. The methodology was methodical and exhaustive. Each treatment that broke down the protein structure of the samples also stopped the disease from spreading. Each treatment that targeted nucleic acids left transmissibility intact.