0In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty revisited Griffith's experiment and concluded that the transforming material was pure DNA, not protein or RNA. These investigators found that DNA extracted from a virulent strain of the bacterium Streptococcus pneumoniae, also known as pneumococcus, genetically transformed an avirulent strain of this organism into a virulent form.
Type IIR cells ⇒ No transformation
Type IIR cells + Type IIIS DNA extract ⇒ Transformation
Type IIR cells + Type IIIS DNA extract + DNase ⇒ No transformation
Type IIR cells + Type IIIS DNA extract + RNase ⇒ Transformation
Type IIR cells + Type IIIS DNA extract + Protease ⇒ Transformation
