In vivo monitoring of cellular signaling and metabolite flux is an essential tool to study the dynamics of cellular networks and the effects of re-engineering these networks. The aims of this proposal are the development and use of a modular, tunable, allosterically controlled biosensor platform that can simultaneously monitor and re-engineer cellular pathways. Small, noncoding RNA molecules (allosteric ribozymes, riboswitches and antiswitches) will be the basis of these biosensors and will be developed to control a fluorescent resonant energy transfer event in response to small molecule ligands or cellular signalling events. In addition, sensor components will be engineered to allow for simultaneous control of expression of endogenous cellular transcripts. A mitogen activated protein kinase pathway from S. cerevisiae will serve as a model system for biosensor development, adaptation, and translational control. These studies are predicted to establish a biosensor platform with rapid detection kinetics that is easily evolvable, modular, and capable of allosteric control of mRNA expression. [unreadable] [unreadable] [unreadable]