Oswald Avery

Oswald Avery (1937)

Oswald Theodore Avery (born October 21, 1877 in Halifax , Nova Scotia , † February 2, 1955 in Nashville , Tennessee ) was a Canadian medic .

He received his PhD from Columbia University in New York City in 1904 . After a phase as a practicing physician, Avery was scientifically active at the Rockefeller Institute of Medical Research from 1913 to 1947. There in 1944, in collaboration with Colin MacLeod and Maclyn McCarty, with the help of an experiment on pneumococci, he was able to provide the first strong evidence that DNA and not, as was previously assumed, proteins are the carriers of genetic information. The three researchers established modern molecular genetics.

Avery was nominated 38 times for a Nobel Prize between 1932 and 1957, but never received it.

The background

Before Avery's experiment, it was unclear which substance class is the carrier of the genetic information. Proteins were generally favored because they are ubiquitous in the cell and are involved in all metabolic functions. The DNA , which is also present in large quantities in the chromosomes , appeared to be less suitable as hereditary substance, as it consists of only four different nucleotides (proteins, however, consist of 20 amino acids ), which also seemed to be present in equal proportions, and their complex structure ( double helix ) still exists was not known.

The attempt

Scheme of the experiment on the "transforming principle"

Avery's experiment took place in 1944 on pneumococci (bacterial pathogens that cause pneumonia). It was based on experiments described by Frederick Griffith in 1928. Griffith worked with two strains of pneumococci, the virulent S-strain, which has a protective mucous capsule that gives the bacterial colony a smooth, shiny appearance and which is therefore called smooth (S), and the nonvirulent R-strain (R36A), Bacteria without a mucous capsule and therefore with a rough surface, which were called rough (R). Griffith injected three groups of mice with different extracts: the first a live R-strain culture, the second heat-killed S pneumococci, and the third both extracts together. The first and second groups did not develop pneumonia. The mice in the third group fell ill and died. A culture of the heart blood of these mice again showed living S-strain pneumococci. As a result, Griffith assumed that the killed S pneumococci contained a transforming substance that can convert the R-type to the S-type.

Dawson and Sia were able to carry out this transformation in vitro and provide the transforming substance in a test tube . Alloway carried out this transformation with an aqueous solution of a cell extract.

Avery and his colleagues Colin MacLeod and Maclyn McCarty at Rockefeller University (then Rockefeller Institute) in New York now wanted to elucidate the chemical nature of the transforming substance ( Transforming Principle ). To do this, they refined the purification process until the result was a cell extract whose proportions of carbon , hydrogen , nitrogen and phosphorus corresponded to those of DNA . To ensure that the transformation was not induced by residues of RNA or proteins , they treated the cell extract with different enzymes prior to transformation. One of these enzymes had deoxyribonucleodepolymerase activity described by Greenstein in 1940 . Only this neutralized the transformation activity of the extract, while trypsin , chymotrypsin (two protein-splitting enzymes ), ribonuclease , protein phosphatases and esterase had no effect on transformation activity. They were also able to show that all of the offspring inherited the S traits and that repeating the experiment with extracts from these offspring led to the same results.

interpretation

This experiment shows that the genetic information must be on the DNA, since the R cells need information from the S cells so that they can form a mucous capsule, i.e. become S cells. And only the DNA made it possible to transform R- to S-cells . In the counterexample with an enzyme, it became even clearer that the genetic information must be in the DNA, since only R cells develop when a DNAse is added because the DNA was broken down by the enzyme.

Membership and Honors

In 1933 Avery was elected to the National Academy of Sciences , in 1936 to the American Academy of Arts and Sciences . In 1945 he received the George M. Kober Medal . In 2004 he was posthumously inducted into the Canadian Medical Hall of Fame .

The Avery lunar crater is named after him.

Publications

• Oswald T. Avery, Rene Dubos : The specific action of a bacterial enzyme on pneumococci of Type III . Science 72 (1930): 151-152, PMID 17838541 .
• Oswald T. Avery, Colin M. MacLeod and Maclyn McCarty: Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Induction of transformation by a deoxyribonucleic acid fraction isolated from pneumococcus type III . In: Journal of Experimental Medicine . Vol. 79, No. 2, 1944, pp. 137-158, PMID 19871359 .
• Maclyn McCarty and Oswald T. Avery: Studies on the chemical nature of the substance inducing transformation of pneumococcal types. II. Effect of deoxyribonuclease on the biological activity of the transforming substance . In: Journal of Experimental Medicine . Vol. 83, No. 2, 1946, pp. 89-96, PMID 19871520 .

literature

• Michaela Scherr, Dietmar Scherr: Milestone in molecular biology: The 'Avery experiment'. In: Biologie in our Zeit 33 (1) (2003), pp. 58-61, ISSN  0045-205X
• Maclyn McCarty: The Transforming Principle - Discovery that Genes are made of DNA , WW Norton Company, 1985, ISBN 0-393-01951-9

Individual evidence

1. ^ Nomination Database. In: nobelprize.org. April 17, 2015, accessed April 17, 2015 . 
2. ^ Members of the American Academy. Listed by election year, 1900-1949 ( PDF ). Retrieved September 27, 2015