Avery, McCarty and MacCleod
In 1944, Oswald Avery, Colin MacCleod and Maclyn McCarty repeated Griffith’s experiment. Instead of using heat-killed bacteria, these scientists isolated protein, carbohydrates, lipids and nucleic acids from the virulent strain and co-injected with the non-virulent bacteria. Carbohydrate extracts were ineffective at transforming bacteria. Protein extracts were incapable of causing transformation. Lipid injections were unable to result in virulence. Only nucleic acid samples treated with RNase were capable of transforming bacteria. When co-injecting with DNase, bacteria were not transformed. Along with Hershey-Chase, this definitiveely illustrated that DNA was the transforming agent capable of transferring genetic information.