An infectious agent can be a protein shape
A prion can transmit disease without carrying its own DNA or RNA. An abnormal conformation of the host prion protein templates further misfolding, building aggregates that damage nervous tissue. Biological information can therefore propagate through molecular shape, although prion strains and transmission remain complex.
Scrapie resisted treatments that normally damage nucleic acids, while procedures affecting proteins reduced infectivity. The ‘protein-only’ hypothesis proposed that the infectious particle was chiefly a misfolded form of a normal host protein. Subsequent genetics, structural work and transmission experiments connected disease susceptibility to the PRNP gene and showed self-propagating conformations. A prion still depends on a host that supplies protein, and cofactors can influence conversion. ‘Without a genome’ does not mean without biological context or variation.
Prions enlarge the category of inheritance. A sequence can be unchanged while a durable protein conformation is copied from molecule to molecule and, in some cases, between organisms. They also explain why ordinary sterilisation assumptions can fail: resistance and infectivity do not follow the rules of bacteria or viruses.
DNA is copied by complementary base pairing. A prion propagates differently: an existing conformation lowers the barrier for compatible protein molecules to adopt a similar fold and join an aggregate. Different stable folds can behave like strains despite sharing an amino-acid sequence. Calling this information is functional—the state biases future states—not a claim that proteins replace genomes for ordinary heredity.
Many disinfection methods are validated against cells or nucleic-acid-bearing agents. Prion aggregates can withstand formalin, heat and radiation conditions that inactivate conventional pathogens, although they are not indestructible. Effective decontamination uses specified combinations of chemicals, temperature and time. The practical lesson is narrow: hazard controls must match the agent’s actual chemistry.
Could an undetected virus still be hiding inside every infectious preparation?
That was a serious historical alternative. Evidence now includes linkage to the host PRNP gene, loss of susceptibility when PrP is absent, generation and amplification of infectious conformations under defined conditions, and structural characterisation of prion fibrils. Cofactors may alter efficiency, but a hidden nucleic-acid genome is not needed to explain replication. The relevant controls were designed precisely to separate that possibility from the reported effect.
Reproducible discovery of a necessary, agent-specific nucleic-acid genome in purified prions would overturn the protein-only core of the model.