Discovering genes are made of DNA

Maclyn McCarty is the sole surviving member of the team that made the remarkable discovery that DNA is the material of inheritance. This preceded by a decade the discovery of the structure of DNA itself. Here he shares his personal perspective of those times and the impact of the double helix. Editor's note — For a long time, biologists thought that 'genes', the units of inheritance, were made up of protein. In 1944, in what was arguably the defining moment for nucleic acid research, Oswald Avery, Maclyn McCarty and Colin MacLeod, at Rockefeller Institute (now University) Hospital, New York, proved that DNA was the material of inheritance, the so-called stuff of life. They showed that the heritable property of virulence from one infectious strain of pneumococcus (the bacterial agent of pneumonia) could be transferred to a noninfectious bacterium with pure DNA1. They further supported their conclusions by showing that this 'transforming' activity could be destroyed by the DNA-digesting enzyme DNAase2,3. This work first linked genetic information with DNA and provided the historical platform of modern genetics. Their discovery was greeted initially with scepticism, however, in part because many scientists believed that DNA was too simple a molecule to be the genetic material. And the fact that McCarty, Avery and MacLeod were not awarded the Nobel prize is an oversight that, to this day, still puzzles.