Explain the biochemical characterization of the transforming principle.

(N/A) Before the work of Avery,MacLeod,and McCarty $(1944)$,it was believed that protein was the genetic material.
These scientists worked to determine the biochemical nature of the 'transforming principle' observed in Griffith's experiment.
They purified biochemicals ($DNA, RNA,$ and proteins) from heat-killed $S$ cells to see which one could transform live $R$ cells into $S$ cells.
They discovered that $DNA$ from the $S$ bacteria was the only substance that caused the transformation of $R$ bacteria.
They observed that digestion with protein-digesting enzymes (proteases) or $RNA$-digesting enzymes $(RNases)$ did not affect the transformation,proving that the transforming substance was neither protein nor $RNA$.
However,digestion with $DNase$ inhibited the transformation process. This confirmed that $DNA$ is the genetic material responsible for transformation.