McCarty, Maclyn (1911- )

American bacteriologist

Maclyn McCarty is a distinguished bacteriologist who has done important work on the biology of Streptococci and the origins of rheumatic fever, but he is best known for his involvement in early experiments which established the function of DNA . In collaboration with Oswald Avery and Colin Munro MacLeod , McCarty identified DNA as the substance which controls heredity in living cells. The three men published an article describing their experiment in 1944, and their work opened the way for further studies in bacteriological physiology, the most important of which was the demonstration of the chemical structure of DNA by James Watson and Francis Crick in 1953.

McCarty was born in South Bend, Indiana. His father worked for the Studebaker Corporation and the family moved often, with McCarty attending five schools in three different cities by the time he reached the sixth grade. In his autobiographical book, The Transforming Principle, McCarty recalled the experience as positive, believing that moving so often made him an inquisitive and alert child. He spent a year at Culver Academy in Indiana from 1925 to 1926, and he finished high school in Kenosha, Wisconsin. His family moved to Portland, Oregon, and McCarty attended Stanford University in California. He majored in biochemistry under James Murray Luck, who was then launching the Annual Review of Biochemistry. McCarty presented public seminars on topics derived from articles submitted to this publication, and he graduated with a B.A. in 1933.

Although Luck asked him to remain at Stanford, McCarty entered medical school at Johns Hopkins in Baltimore in 1933. He was married during medical school days, and he spent a summer of research at the Mayo Clinic in Minnesota. After graduation, McCarty spent three years working in pediatric medicine at the Johns Hopkins Hospital. Even in the decade before penicillin , new chemotherapeutic agents had begun to change infectious disease therapy. McCarty treated children suffering from Pneumococcal pneumonia , and he was able to save a child suffering from a Streptococcal infection, then almost uniformly fatal, by the use of the newly available sulfonamide antibacterials. Both of these groups of bacteria , Streptococcus and the Pneumococcus, would play important roles throughout the remainder of McCarty's career.

McCarty spent his first full year of medical research at New York University in 1940, in the laboratory of W. S. Tillett. In 1941, McCarty was awarded a National Research Council grant, and Tillett recommended him for a position with Oswald Avery at the Rockefeller Institute, which was one of the most important centers of biomedical research in the United States. For many years, Avery had been working with Colin Munro MacLeod on Pneumococci. In 1928, the British microbiologist Frederick Griffith had discovered what he called a "transforming principle" in Pneumococci. In a series of experiments now considered a turning point in the history of genetics, Griffith had established that living individuals of one strain or variety of Pneumococci could be changed into another, with different characteristics, by the application of material taken from dead individuals of a second strain. When McCarty joined Avery and MacLeod, the chemical nature of this transforming material was not known, and this was what their experiments were designed to discover.

In an effort to determine the chemical nature of Griffith's transforming principle, McCarty began as more of a lab assistant than an equal partner. Avery and MacLeod had decided that the material belonged to one of two classes of organic compounds: it was either a protein or a nucleic acid. They were predisposed to think it was a protein, or possibly RNA , and their experimental work was based on efforts to selectively disable the ability of this material to transform strains of Pneumococci. Evidence that came to light during 1942 indicated that the material was not a protein but a nucleic acid, and it began to seem increasingly possible that DNA was the molecule for which they were searching. McCarty's most important contribution was the preparation of a deoxyribonuclease which disabled the transforming power of the material and established that it was DNA. They achieved these results by May of 1943, but Avery remained cautious, and their work was not published until 1944.

In 1946, McCarty was named head of a laboratory at the Rockefeller Institute which was dedicated to the study of the Streptococci. A relative of Pneumococci, Streptococci is a cause of rheumatic fever. McCarty's research established the important role played by the outer cellular covering of this bacteria. Using some of the same techniques he had used in his work on DNA, McCarty was able to isolate the cell wall of the Streptococcus and analyze its structure.

McCarty became a member of the Rockefeller Institute in 1950; he served as vice president of the institution from 1965 to 1978, and as physician in chief from 1965 to 1974. For his work as co-discoverer of the nature of the transforming principle, he won the Eli Lilly Award in Microbiology and Immunology in 1946 and was elected to the National Academy of Sciences in 1963. He won the first Waterford Biomedical Science Award of the Scripps Clinic and Research Foundation in 1977 and received honorary doctorates from Columbia University in 1976 and the University of Florida in 1977.

See also Microbial genetics; Microbiology, clinical; Streptococci and streptococcal infections