The resemblance between the discoveries that
DNA is the basis of heredity and that
prions are infectious
proteins is remarkable. Though four decades separated these two discoveries, the biochemical methodologies and scientific philosophies that were employed are surprisingly similar. In both cases, bioassays available at the time that the projects were initiated proved to be inadequate to support purification studies. Improved bioassays allowed the transforming principle (TP) to be purified from pneumococci and
prions from
scrapie-infected hamster brains. Publications describing TP as composed of
DNA prompted some scientists to contend that undetected
proteins must contaminate TP enriched fractions. The simplicity of
DNA was thought to prevent it from encoding genetic information. By the time
prions were discovered, the genomes of all infectious pathogens including viruses, bacteria, fungi and parasites had been shown to be comprised of
nucleic acids and so an antithetical refrain became widely echoed:
DNA or
RNA molecules must be hiding among the
proteins of
prions. Finding the unexpected and being asked to demonstrate unequivocally the absence of a possible contaminant represent uncanny parallels between the discoveries that
DNA encodes the genotype and that
prions are infectious
proteins.