Filonov, G.S. et al. J. Am. Chem. Soc. 136, 16299–16308 (2014).

RNA mimics of GFP, such as Spinach, allow RNAs to be tagged analogously to protein tagging with GFP. These RNA aptamers function by binding and activating fluorescence of an analog of the GFP chromophore. The discovery of such aptamers has proven difficult because not all RNAs that can bind the chromophore can also activate its fluorescence. Filonov et al. describe a FACS-based method for discovering bright aptamers. In this approach, RNAs that can bind the chromophore are expressed in Escherichia coli and sorted for brightness. The approach yielded Broccoli, which is brighter than Spinach2 in both bacteria and mammalian cells. This method for identifying new aptamers and the addition of Broccoli to the RNA imaging toolbox can potentially improve live-cell imaging of RNAs.