Maclyn McCarty (June 9, 1911 – January 2, 2005)[1] was an American geneticist, a research scientist described in 2005 as "the last surviving member of a Manhattan scientific team that overturned medical dogma in the 1940s and became the first to demonstrate that genes were made of DNA."

[2] McCarty devoted his life as a physician-scientist to studying infectious disease organisms, and was best known for his part in the monumental discovery that DNA, rather than protein, constituted the chemical nature of a gene.

Uncovering the molecular secret of the gene in question — that for the capsular polysaccharide of pneumococcal bacteria — led the way to studying heredity not only through genetics but also through chemistry.

As an undergraduate at Stanford University, he began his studies in the nascent field of biochemistry, working with James Murray Luck on protein turnover in the liver.

[3] McCarty's arrival at Rockefeller University was also marked by another milestone, namely, the development of a reagent assay to positively correlate DNA with biological activity.

Together with his students and collaborators, over the next 20 years, McCarty's work changed the understanding of the organism from a gram-positive streptococcus with a particular serological characteristic to one of the best characterized bacterial species.

McCarty further demonstrated the precise configuration of the hexosamine linkage by synthesizing both α- and β-N-acetyl-glucosamine ovalbumin and showing that only the second reacted with group A antisera.

In parallel, McCarty studied patients with rheumatic fever admitted to the Rockefeller Hospital as well as valuable specimen collections from military outbreaks of the disease during World War II.

He found that group A streptococci secreted unusually high amounts of DNase, and established a test for the detection of antibodies produced in response to this antigen.

Along with his second[1] wife, Marjorie, McCarty had a wide circle of very close friends, both in the United States and abroad, who cherished his personal warmth, his low key, spare, and pragmatic character, his wit, and his wide-ranging intellect.