Maclyn McCarty, 1940s
In 1941 Maclyn McCarty joined the laboratory and aided Avery in his research. Avery and McCarty focused first on purifying the transforming substance. They soon determined that the substance was rich in nucleic acids, but ribonuclease, an enzyme discovered by René Dubos that destroys ribonucleic acid (RNA), did not inactivate the substance. Further, the transforming substance had a high molecular weight and gave a strong reaction to the Dische diphenylamine test, which detects for the presence of DNA. Consequently Avery and McCarty concluded that the transforming substance, which produced permanent, heritable change in an organism, was DNA.