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).

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.

Bacteria have an interesting answer. Attenuation, or dampening, of the trp operon is made possible by the fact that the rate of translation influences RNA structure, which in turn influences the ...