Oswald Avery

Oswald Theodore Avery, (Halifax, October 21, 1877 - February 2, 1955). Canadian physician and researcher, he studied at Columbia University and almost all his work was done at The Rockefeller Institute Hospital in New York, United States. He was one of the first molecular biologists and a pioneer in the field of immunochemistry, although he is best known for his discovery in 1944, along with his collaborators Maclyn McCarty and Colin MacLeod, that DNA (deoxyribonucleic acid) is the material from which genes and chromosomes are formed and how these define the sexuality of the human being. It was previously believed that proteins were the carriers of genes.

It was a continuation of the work of Frederick Griffith in 1928. In turn, Alfred Hershey and Martha Chase continued this work in 1952 with the Hershey-Chase experiment.

Experiment performed by Avery

Avery, Colin MacLeod, and Maclyn McCarty did a series of experiments using strains of pneumococcus bacteria, which cause pneumonia. Pneumococci grow in the host body, but, like other types of bacteria, they can also grow on solid or liquid surfaces.

Pneumococci are bacteria that, when they do not have a capsule, grow in the laboratory, forming colonies with a rough surface; if they have that envelope, their appearance becomes smooth. The difference might seem like an aesthetic trifle, but it's not. According to data from Avery's laboratory, precisely the capsule is the cause of virulence.

Frederick Griffith discovered that by injecting mice with small doses of avirulent pneumococci along with large amounts of pathogenic but heat-killed pneumococci, the animals not only die of pneumonia but also show live encapsulated bacteria in their blood. In other words, under these experimental conditions, the non-virulent pneumococcus acquires the information to synthesize the capsule (it transforms, Griffith would say) in the body of the mouse and, with it, the capacity to produce disease.

Griffith concluded that there was some "principle" that turned rough (R) strains into smooth (S) ones with a sugar coat. When Avery read Griffith's results and became interested in identifying this "transformative principle," Avery and his team began experimenting using a test tube instead of a mouse. They used detergent to break down the heat-killed smooth cells by creating a lysis out of them. They then used this lysis for transformation assays. The tubes worked well and showed that lysis of heat-killed S could change (R)Rough to (S)Smooth. The transforming principle was somewhere in the lysis.

They tested each of the lysis components for transforming activity. They first incubated the lysed heat-killed smooth strain with an enzyme, SIII, which completely consumes the sugar coat. Lysis of uncoated smooth strain was still useful for transforming. This revealed to them that the R strains did not create a new coat from the smooth strain coat parts. They then incubated the uncoated smooth strain lysis with protein-digesting enzymes (trypsin and chymotrypsin) and then tested the ability of this lysis to transform. This protein-free lysis was still transforming, so the transforming principle was not protein.

When they wanted to test and purify the lysis, they precipitated the nucleic acids – DNA and RNA – with alcohol. They were the first to isolate the nucleic acids of a pneumococcus. When they saw that the transforming "start" was not in the sugar shell, nor in the protein, they suspected that it might be in one of the nucleic acids.

They dissolved the mixture with alcohol in water, first they destroyed the RNA with the RNase enzyme, they tested the transforming capacity of this solution, the solution still had the capacity to transform, in such a way that the RNA could not be the transforming "start". When they had left virtually pure DNA, as a final test, they incubated the solution with the DNA-digesting enzyme, Dnase. They tested the transformative capacity of this solution, which was unable to transform. Avery and his team concluded that DNA was the transforming principle and published their results in 1944.

Eponymy

• In 1976 it was decided in his honor to call "Avery" a lunar crater.