Cell Genetics

François Jacob conducted all of his research in the laboratories of the Pasteur Institute, even after his election to the Collège de France.

His scientific work can be divided into three periods:

• From 1950 to 1958, he focused on the study of bacterial lysogeny (the state of a bacterium that has incorporated part of a bacteriophage’s genetic material) and on the concept of the provirus or prophage, a dormant genome integrated into that of the host bacterium.
  Together with Élie Wollman, he also conducted research on bacterial conjugation, work that led to the 1961 publication of their book Sexuality and the Genetics of Bacteria.
• From 1958 to 1970, as their research converged, he teamed up with his colleague at the Pasteur Institute, Jacques Monod, to explore the idea that the control of enzyme expression levels in cells results from the regulation of DNA sequence transcription.
  In 1958, the PaJaMo experiment (short for Pardee–Jacob–Monod) demonstrated that bacteria synthesize an inhibitor to suppress the production of beta-galactosidase.
  Jacob and Monod eventually demonstrated gene regulation in Escherichia coli and formulated the operon model, foreshadowing the existence of messenger RNA. In 1965, they were awarded the Nobel Prize, along with André Lwoff, for the discovery of the mechanism of protein synthesis and the regulatory system governing this synthesis.
• From 1970 to 1991, François Jacob worked on teratocarcinoma and mouse embryos. His goal was to understand, at the molecular level, the complexity of higher organisms, embryonic development, and cancer.

His lectures at the Collège de France (1964–1991) reflected all of this research.

The final decades of his life were devoted to publishing works on the history and epistemology of science, whose influence remains significant ( *La Logique du vivant*, *Le Jeu des possibles*, and *La Souris, la Mouche et l’Homme* ).

Biographical note written by Ronan Le Guen (Collège de France).