Grunberg-Manago studied biochemistry and, in 1955, while working in the lab of Spanish-American biochemist
Severo Ochoa, she discovered the first nucleic-acid-synthesizing
enzyme. Initially, everyone thought the new enzyme was an
RNA polymerase used by
E. coli cells to make long chains of RNA from separate nucleotides. Although the new enzyme could link a few
nucleotides together, the reaction was highly reversible and it later became clear that the enzyme,
polynucleotide phosphorylase, usually catalyzes the
breakdown of RNA, not its synthesis. Nonetheless, the enzyme was extraordinarily useful and important. Almost immediately,
Marshall Nirenberg and
J. Heinrich Matthaei put it to use to form the first three-nucleotide RNA
codons, which coded for the
amino acid phenylalanine. This first step in cracking the
genetic code entirely depended on the availability of Grunberg-Manago’s enzyme. In 1959, Ochoa and
Arthur Kornberg won the 1959
Nobel Prize in Physiology or Medicine "for the synthesis of the nucleic acids RNA and DNA." She was elected a Foreign Honorary Member of the
American Academy of Arts and Sciences in 1978, a Foreign Associate Member of the
National Academy of Sciences in 1982, and an International member of the
American Philosophical Society in 1992. Grunberg-Manago was the first woman president of the
International Union of Biochemistry (1985–1988), and she was also the first woman to preside over the
French Academy of Sciences (1995–1996). ==Later life and death==