In the 1944 Avery–MacLeod–McCarty experiment, which bacterial substance was destroyed by DNase?

In the 1944 Avery–MacLeod–McCarty experiment, DNase destroyed the transforming DNA.

Oswald Avery, Colin MacLeod, and Maclyn McCarty investigated transformation in pneumococcal bacteria. Extracts from virulent bacteria could convert harmless bacteria into a virulent form. The researchers purified the active material and tested whether enzymes that destroy proteins, RNA, or DNA would eliminate its transforming ability.

Proteases and RNase did not stop transformation, but DNase did. This showed that DNA was the substance responsible for carrying the heritable change. The result was a major step toward identifying DNA as genetic material.

The wording matters: the experiment did not show that every detail of heredity was understood, nor did it immediately convince all scientists. Many researchers still favored proteins because they seemed chemically more varied. Alfred Hershey and Martha Chase’s 1952 bacteriophage experiment later provided independent evidence that DNA, rather than protein, enters bacteria during infection.