Genetic control by a metabolite binding mRNA.

Messenger RNAs are typically thought of as passive carriers of genetic information that are acted upon by protein- or small RNA-regulatory factors and by ribosomes during the process of translation. We report that the 5'-untranslated sequence of the Escherichia coli btuB mRNA assumes a more proactive role in metabolic monitoring and genetic control. The mRNA serves as a metabolite-sensing genetic switch by selectively binding coenzyme B(12) without the need for proteins. This binding event establishes a distinct RNA structure that is likely to be responsible for inhibition of ribosome binding and consequent reduction in synthesis of the cobalamin transport protein BtuB. This finding, along with related observations, supports the hypothesis that metabolic monitoring through RNA-metabolite interactions is a widespread mechanism of genetic control.