Riboswitches are structured RNAs that bind metabolites and, dependent on this binding, control gene expression. In most cases, the metabolite binding acts as a simple "on-off" switch. Now Sudarsan et al. report tandem riboswitch architectures that facilitate more sophisticated control. The 5′ untranslated region of Bacillus clausii metE RNA includes two riboswitches that respond independently to two different metabolites to function as a two-input Boolean NOR logic gate.
N. Sudarsan, M. C. Hammond, K. F. Block, R. Welz, J. E. Barrick, A. Roth, R. R. Breaker, Tandem riboswitch architectures exhibit complex gene control functions. Science 314, 300-304 (2006). [Abstract] [Full Text]