On this day, April 19, 2013, Francois Jacob, a war hero and biologist who would win a Nobel for his work on genetic expression, died at age 92.
- 1927: Nobelist who cracked DNA-protein code is born
- The Jew who would become France’s top Catholic is baptized
- 1945: Danny the Red or Green is born, will upset France
Francois Jacob was born on June 17, 1920 in Nancy, northeastern France, the only child of merchant Simon Jacob and Therese (nee Franck). The family moved to Paris during his childhood. Jacob, something of a prodigy, studied at the Lycee Carnot high school – which he reportedly hated.
Following school, he entered medical studies at the Faculty of Paris, apparently less because he felt the urge to heal his fellow man and more because he was horrified at the thought of more confinement, in science classes at the local Polytechnique.
Before Jacob could finish medical school, in 1939, World War II broke out. Germany occupied France, his mother died and he went to England to join the Allies. In 1940 he joined the medical company of the French 2nd Armored Division, commanded by Charles de Gaulle. After fighting in North Africa he returned to France, where he was injured during a German air raid in 1944 and spent seven months in hospital.
His conduct during the war won him several medals for heroism and valor, including the Légion d'honneur and Croix de Liberation. But because of his injuries to his hands, which precluded a career in surgery, he stopped practicing medicine – though he finally received his medical credentials in 1947, and devoted himself to research. That same year, he married his first wife, Lysiane Bloch, with whom he would have four children.
In 1954, the year after James Watson sand Francis Crick published their groundbreaking study on the structure of DNA, Jacob earned his doctorate in science at the Sorbonne, writing about bacteria in which viruses called phages surreptitiously exist as dormant DNA. (The viral genes usually integrate with the bacteria's own genes. Sometimes the alien DNA simply floats in the bacterial plasma).
Within two years, in 1956, he was appointed head of laboratory at the renowned Pasteur Institute and in 1960, he took over its spanking new department of cellular genetics.
Give a germ a bowl of milk
In 1961, he and biochemist Jacques Monod wondered how germs turn their genes on and off. Specifically, they studied how bacteria increase or decrease the presence of enzymes (active proteins) when conditions change. They concluded that enzyme levels are a factor of genetic expression.
In other words, when conditions change, something tells the DNA, "make more of enzyme X and less of enzyme y".
For instance, if a bacterium was put in chicken soup, it would quickly produce different enzymes than if put in a glass of milk.
Working with Monod on bacteria given dairy to eat, Jacob discovered that specific proteins inside cells affect whether genes for enzymes are expressed or not.
The result was the "repressor model," which goes like this. The bacteria with which they worked routinely produces a protein that represses the production of enzymes digesting lactose. The repressor binds to the DNA at the site of the lactose enzyme gene, preventing the gene from being expressed.
That prevents the production of enzymes that digest lactose. This goes on until the bacteria eats dairy, which contains lactose. The lactose binds to the repressor, which falls off the DNA. The enzyme to digest lactose can then be produced. The lactose is digested and the repressor binds back to the DNA, and so on.
The principle of the E. coli, the repressor and the dairy habit was extrapolated to a great many molecular mechanisms, though it proved to be extremely oversimplified in many cases, and birthed the science of molecular biology.
The threesome of Jacob, Monod and their colleague at Pasteur, the microbiologist Andre Lwoff, also discovered messenger RNA – the molecule that "reads" DNA and carries the message to the ribosomes that actually build the proteins inside our cells.
In 1965, Jacob shared the Nobel Prize in Physiology or Medicine with Monod and with Lwoff, for their discovery that cells can switch genetic information on and off.
Having broken ground on genetic expression, Jacob turned his attention to cancer, which also turns out to have substantial genetic causes. He died on April 9, 2013, in Paris.