Oswald Avery

Oswald Theodore Avery ( born October 21, 1877 in Halifax, Nova Scotia; † February 2nd 1955 in Nashville, Tennessee) was a Canadian physician. He received his Ph.D. at Columbia University in New York City in 1904. After a period as a practicing physician Avery was 1913-1947 at the Rockefeller Institute of Medical Research scientifically active. In the years 1929/1930 he was president of the American Association of Immunologists.

There he was in 1944 in collaboration with Colin MacLeod and Maclyn McCarty with the help of an elegant experiment to pneumococcal provide a first strong indication that the DNA and the way we thought until then, proteins are not carriers of genetic information. The three researchers reasoned thus the modern molecular genetics.

The background

Prior to Avery's trial was unclear what substance class carrier of genetic information. General proteins were favored because they are ubiquitous in the cell and involved in all metabolic functions. The also present in large quantities in the chromosomes DNA appeared as genetic material less suitable, since it consists of only four different nucleotides (proteins, however, of 20 amino acids ), which seemed also to be present in equal proportions, and its complex structure (double helix) still was not known. Avery developed an ingeniously simple in its explanatory power but exact test, which is considered excellent example of logical experimentation today.

The attempt

The attempt took place at Avery's Pneumococcus ( bacterial pathogens of pneumonia ) 1944. It was based on experiments described in 1928 Frederick Griffith. Griffith worked with two strains of pneumococci, the virulent S strain, which has a protective slime capsule that gives a smooth, shiny appearance of the bacterial colony and was therefore smooth (S ) above, and the nonvirulenten R strain ( R36A ) slime bacteria without capsule and therefore with a rough surface, which was designated rough (R). Griffith injected mice a living R strain culture along with heat-killed S pneumococci, after which the mice died and a culture of heart blood of these mice again showed living S strain pneumococci.

Dawson and Sia were able to perform this transformation in vitro. Alloway led this transformation with cell extract.

Avery and his colleagues Colin MacLeod and Maclyn McCarty at the Rockefeller University (then called the Rockefeller Institute ) in New York wanted to now the chemical nature of the transforming substance ( Transforming Principle ) explain, by treating the cell extract prior to transformation with different enzymes. One of these enzymes had one, described by Greenstein 1940 Desoxyribonucleodepolymerase activity. Only that the transforming activity of the extract neutralized, while trypsin, chymotrypsin, ribonuclease, phosphatase and esterase were without effect with respect to transformation activity. You could also demonstrate that all progeny inherit the S- properties and that the repetition of the experiment with extracts from these descendants led to the same results.

Interpretation

This experiment proves that the genetic information on the DNA must occur, since the R- cell information from the S cells needed so that they form a slime capsule can become S- cells ie. And only the DNA made ​​it possible to transform the R- to S- cells. When a counter-example with an enzyme became more apparent that the genetic information in DNA must be, since with the addition of a DNAse develop only R cells because the DNA was degraded by the enzyme.

Publications

• The specific action of a bacterial enzyme on pneumococci of Type III. Science 72 (1930 ) :151 -152
• 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 19,871,359th
• 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 19,871,520th