Avery's experiment: DNA was the transforming agent.

In the 1940s, Oswald T. Avery, Colin MacLeod, and Maclyn McCarty showed that DNA was responsible for transformation.

§ They used enzymes that hydrolysed polysaccharide, DNA, RNA, and protein on samples of the disease-causing strain-S pneumococci.

§ Different samples had different parts of their cells destroyed by these enzymes.

§ The researchers then exposed strain-R pneumococci to the treated samples of strain S.

§ The transformation of strain R to strain S was blocked only when the DNA in the sample was destroyed.

These results provided strong evidence that DNA carried genetic information for transformation. However, many scientists remained unconvinced.