Lactose isn’t present in our guts all the time. To ingest it and other occasional sources of nutrition, Escherichia coli must detect the molecules and then make the proteins that help harvest them.

That process of on-demand protein production is an example of gene regulation. Without gene regulation, an organism’s genetic code would remain an unread list of unmade proteins. Gene regulation controls when and where proteins are made and in what quantities.

Nature has evolved several modes for gene regulation, some of which involve casts of multiple molecular actors. Among the simplest are two modes used by E. coli to make the best use of randomly available sources of food. How those two modes evolved is the subject of a new analysis by physicists Ulrich Gerland of the University of Munich in Germany and Terence Hwa of the University of California, San Diego. 1  

The two modes are depicted...

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