picoFAST: New Genetically Encoded Fluorescent Tag

Objective: Design of a small fluorogen-activating protein picoFAST. Methods: Protein expression and purification were performed. In vitro screening with the new protein was held, the optical properties were studied. Widefield fluorescence microscopy of live cells was performed. Results and Discussion: We discovered that the N-fragment of split nanoFAST can act as a fluorogen-activating protein in complex with HBR-DOM2 in the absence of the C-fragment, and we called it picoFAST. We demonstrated that the picoFAST protein in complex with HBR-DOM2 fluorogen can be used for fluorescent labeling of individual compartments of live HeLa Kyoto cells. Conclusions: We designed the smallest fluorogen-activating protein picoFAST and showed that it can be used in pair with HBR-DOM2 as a genetically-encoded fluorescent tag in live cells.