Reversible control of the circadian clock using translational switching of the core clock gene, Cry1. Using the hSynapsin promoter (Synapsin I), expression of Cry1::EGFP was restricted to neurons that expressed the required orthogonal tRNA synthetase (marked by coexpressed mCherry protein) and the tRNA_CUA under the hU6 promoter. Cry1::Egfp mRNA was controlled by its own minimal promoter (pCry1), which directs its rhythmic transcription. Translational of Cry1::EGFP was strictly conditional on the presence of AlkK, an ncAA that is inserted into the protein upon readout of an amber stop codon (i.e., UAG). Circadian rhythms were monitored before and after AlkK administration with Per2::Luc bioluminescence in SCN explants or behavioral analysis in mice.