17 June 1920|
|Died||19 April 2013
|Notable awards||1965 Nobel Prize in Physiology or Medicine|
Like his colleague Monod, Jacob was an almost lifelong atheist.
- import lactose,
- cut lactose to its constituents glucose and galactose, and
- convert the galactose to glucose.
It was known that cells increase the enzymes for these steps when exposed to lactose.
With work on DNA, it became clear that all proteins were being produced from their genetic code. Jacob and Monod demonstrated that, in the bacterium E. coli), there are specific proteins that repress the transcription of the DNA to its product (RNA. This reduces the production of those particular enzymes.
The lac repressor
The lac repressor is a DNA-binding protein which inhibits the expression of genes which code for lactase enzymes. The repressor is active in the absence of lactose.
This repressor (the lac repressor) is made in all cells. It binds directly to DNA at the genes it controls, and physically prevents transcription. When lactose becomes available, it is converted into allolactose, which inhibits the lac repressor's DNA binding ability.
In this way, a robust feedback loop is constructed that allows the set of lactose-digesting enzymes to be made only when they are needed.
The regulation of gene activity has developed into a very large sub-discipline of molecular biology. There are many mechanisms and many levels of complexity. Current researchers find regulatory events at every level of the processes that express genetic information. In the relatively simple genome of baker's yeast, (Saccharomyces cerevisiae), 405 of its 6,419 protein-encoding genes are directly involved in transcriptional control, compared to 1,938 that are enzymes.
- Sexuality and the genetics of bacteria by E.L. Wollmann and François Jacob, published by Academic Press, 1961
- The possible & the actual by François Jacob, published in the United States by Pantheon Books, and in Canada by Random House of Canada, 1982
- The logic of life by François Jacob, translated from the 1976 French edition by Princeton University Press 1993
- Of flies, mice and men by François Jacob, translated from the French edition and published by Harvard University Press, 1998
François Jacob Facts for Kids. Kiddle Encyclopedia.