Lac operon

The lac operon consists of three adjacent genes required for the transport and of lactose (milk sugar) in the Escherichia coli (E. coli) and some other bacteria. The term operon is used when genes (in this case lacZYA) are co-transcribed into a single messenger RNA. The lac operon is regulated by several factors, one of which is the availability of lactose as an energy source. Control of the lac genes was the first genetic regulatory mechanism to be elucidated, one reason for this is that it is one of the simplest, at least in outline, consisting of simple negative (lac repressor) and positive (CAP) regulatory elements. The lac operon has been considered the canonical example of prokaryotic gene regulation.

Nobel Prize

For their work in elucidating lac regulation, Jacques Monod and Francois Jacob, working at the Pasteur Institute in Paris, received the Nobel Prize in Physiology or Medicine in 1965. In addition to the first discovery of a genetic regulator (the repressor) and its site of action on DNA (the operator), other fundamental insights from their work include:

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Nobel Prize - 1965

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• the discovery of co-regulation of the lac genes
• the invention of genetic tools both for selecting and classifying mutants defective in either repressor or operator
• the distinction between negative and positive regulation
• the discovery of lactose analogs that are substrates for beta-galactosidase but not inducers and others which are inducers but not substrates.

The last point was critical in separation of prior speculations from modern models of genetic control.

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