In the experiment by Avery, McLeod, and McCarty, what substance was identified as the transforming substance?

In the groundbreaking experiment conducted by Avery, McLeod, and McCarty, DNA was identified as the transforming substance responsible for conveying genetic information. This work built upon the earlier findings of Frederick Griffith, which indicated that a "transforming principle" could change the properties of bacteria.

In their experiments, Avery and his colleagues systematically isolated various components of the bacterial cell, including proteins, RNA, and DNA, to determine which was responsible for the transformation observed in Griffith's work. They found that only DNA was capable of transforming non-virulent bacteria into virulent ones, establishing that DNA carries the genetic information necessary for heredity.

This conclusion was pivotal because it shifted the scientific consensus towards DNA as the molecule that constitutes the genetic material, laying the foundation for modern genetics. The clarity of evidence presented through their experiments demonstrated that when they added purified DNA from virulent strains to non-virulent strains, the latter captured and expressed the virulent characteristics, definitively linking DNA to heredity and genetic transformation.