Who revealed the biochemical nature of the transforming principle? How was it done?
Oswald Avery, Colin MacLeod and Maclyn McCarty (1933 - 1944) conducted experiments to reveal the biochemical nature of the transforming principle.
They purified biochemical (proteins, DNA and RNA) form the heat-killed S cells. They wanted to see which one of them was able to transform the R strain. So, they discovered that protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect transformation, but DNase inhibits transformation. Thus, they concluded that it was the DNA which was able to transform the R strain.