Marshall W. Nirenberg

Marshall Warren Nirenberg
Nirenberg in 2003
Born	April 10, 1927 (1927-04-10) New York City
Died	January 15, 2010(2010-01-15) (aged 82) New York City
Nationality	United States
Fields	Biochemistry
Institutions	National Institutes of Health
Alma mater	University of Florida University of Michigan
Known for	ฺContribution to solving the genetic code
Influences	T. Mooreguero
Notable awards	NAS Award in Molecular Biology (1962) National Medal of Science (1964) Gairdner Foundation International Award (1967) Albert Lasker Award for Basic Medical Research (1968) Nobel Prize in Physiology or Medicine (1968) Franklin Medal (1968) Louisa Gross Horwitz Prize (1968)
Spouse	Perola Zaltzman-Nirenberg (1961-2001; her death) Myrna M. Weissman (m. 2005-2010; his death)

Marshall Warren Nirenberg (April 10, 1927 – January 15, 2010) was an American biochemist and geneticist. He shared a Nobel Prize in Physiology or Medicine in 1968 with Har Gobind Khorana and Robert W. Holley for "breaking the genetic code" and describing how it operates in protein synthesis. In the same year, together with Har Gobind Khorana, he was awarded the Louisa Gross Horwitz Prize from Columbia University.

By 1958, experiments and analysis such as the Avery–MacLeod–McCarty experiment, the Hershey–Chase experiment, the Watson–Crick structure and the Meselson–Stahl experiment had shown DNA to be the molecule of genetic information. It was not known, however, how DNA directed the expression of proteins, or what role RNA had in these processes. Nirenberg teamed up with Heinrich J. Matthaei at the National Institutes of Health to answer these questions. They produced RNA composed solely of uracil, a nucleotide that only occurs in RNA. They then added this synthetic poly-uracil RNA into a cell-free extract of Escherichia coli which contained the DNA, RNA, ribosomes and other cellular machinery for protein synthesis. They added DNase, which breaks apart the DNA, so that no additional proteins would be produced other than that from their synthetic RNA. They then added 1 radioactively labeled amino acid, the building blocks of proteins, and 19 unlabeled amino acids to the extract, varying the labeled amino acid in each sample. Only in the extract containing the radioactively labeled phenylalanine, was the resulting protein also radioactive. This implied that the genetic code for phenylalanine on RNA consisted of a repetition of uracil bases. Indeed, as we know now, it is UUU (three uracil bases in a row). This was the first step in deciphering the codons of the genetic code and the first demonstration of messenger RNA (see Nirenberg and Matthaei experiment).