Chapter 6 : Le Labo de Jacques

Abstract:

On arriving at the Pasteur Institute, the author told Jacques Monod that he had come there to learn about adaptive enzymes and that he wished him to suggest a problem for him to work on. As a matter of fact, a strong candidate for a “preenzyme” had already been found in noninduced E. coli by Mel Cohn and Annamaria Torriani. Cohn and Torriani had shown that there was present in extracts from noninduced cells an enzymatically inactive protein which they called Pz. This protein cross-reacted with antibodies raised in rabbits by immunization with purified β-galactosidase (Gz). The experiment that Jacques proposed was indeed very simple. He had recently received a series of twenty auxotrophic mutants of E. coli from Bernard Davis, each requiring a different amino acid or accessory factor for growth. Enzyme synthesis began almost immediately upon adding back the required amino acid or growth factor. At this time, the kinetics of enzyme production were being followed as a function of time. It seemed to the author that if growth were indeed required, enzyme production should be measured with respect to the increase in bacterial mass. The final and complete elimination of the Pz protein as a precursor having anything to do with induction of β-galactosidase synthesis came a few years later when Cohn, Lennox, and Spiegelman transduced the lacZ gene into an i+z- Shigella dysenteriae containing no Pz, and obtained lac+ recombinant Shigella.