When Avery and his colleagues had obtained what was concluded to be the transforming factor from the IIIS virulent cells, they treated the fraction with proteases, RNase, and DNase, followed in each case by the assay for retention or loss of transforming ability. What were the purpose and results of these experiments? What conclusions were drawn?

Key Concepts

Transforming Principle

The transforming principle refers to the substance responsible for genetic transformation, which was identified by Avery and his colleagues as DNA. In their experiments, they demonstrated that DNA from virulent IIIS cells could transform non-virulent IIR cells into virulent forms, indicating that DNA carries genetic information.

Enzymatic Treatment

Avery's team used specific enzymes—proteases, RNase, and DNase—to treat the transforming factor. Proteases degrade proteins, RNase degrades RNA, and DNase degrades DNA. By observing which treatments resulted in the loss of transforming ability, they could determine which macromolecule was responsible for the transformation.

Conclusion of Avery's Experiments

The results of Avery's experiments showed that only the treatment with DNase led to the loss of transforming ability, confirming that DNA was the transforming factor. This pivotal conclusion provided strong evidence that DNA, not protein or RNA, is the genetic material in organisms, laying the groundwork for modern genetics.