Shelby is an assistant editor for The Scientist. She earned her PhD from West Virginia University in immunology and microbiology and completed an AAAS Mass Media fellowship.

The operon is regulated by Lac repressor, the product of the lacI gene, which is transcribed from its own promoter (PI). The repressor inhibits transcription by binding to the lac operator (O).

For example, repression of the lac operon by its repressor, called lacI, is inhibited by the ligand allolactose, to which the repressor protein directly binds. Thus, lactose, from which ...