The Avery, MacLeod and McCarty Research on Heredity and DNA Genetics
Genetic research in the twentieth century had benefited immensely from Frederick Griffith's 1928 Transformation experiment. This experiment had shown that pneumococcus bacterial strains, far from having fixed and non-interchangeable properties, were capable of transformation. Genetic information could be transformed from the virulent bacterial strain to the non-virulent one, conferring the latter with virulent properties, and this transformation could be passed on to succeeding bacterial generations.
This clearly indicated gene transfer, but Griffith, and for many years several researchers after him, remained in the dark about how this transformation happened and about where the genetic information was stored in the chromosomes.
Eukaryote chromosomes consist of proteins and nucleic acids that are composed of, respectively, 20 different amino acids and 4 different unitary building blocks. Since the number of amino acids is higher, it was thought that the diverse genetic information was more likely to be contained in the proteins.
Then Oswald Avery and his colleagues at the Rockefeller Institute, Colin MacLeod and Maclyn McCarty, followed up on Griffith's research, and discovered that -
It was the DNA that contained the genetic information.
- It was the DNA transfer from the virulent to the non-virulent strains that brought about the transformation process.
They were able to discover this by using refined chemical compound extraction and isolation techniques and doing the following -
- They removed the proteins from the virulent bacterial cells using protease enzymes, and then placed the cells in the non-virulent bacterial culture. The non-virulent bacteria transformed and became virulent. Since the proteins were missing, this meant that the genetic information was not contained in the proteins.
- They then removed the DNA from the virulent bacterial cells using a deoxyribonuclease enzyme, and then placed the cells in the non-virulent bacterial culture. The non-virulent bacteria failed to transform. This meant that the genetic information was contained in the DNA.
In 1944, they published an account of their experiment in Journal of Experimental Medicine. It aroused much interest, but their conclusion on DNA was questioned. Then, in 1952, Alfred Hershey and Martha Chase in their bacterial phage research work proved conclusively that DNA was indeed the carrier of hereditary matter. The year after that, in 1953, James Watson and Francis Crick discovered the DNA double helix structure.
Avery's role in DNA research is an important one and he received many honors and acknowledgments, but, strangely, in one of their biggest oversights, the Nobel Prize Committee failed to consider him for the Nobel Prize.