A straightforward approach for bioorthogonal labeling of proteins and organelles in live mammalian cells, using a short peptide tag

In the high-resolution microscopy era, genetic code expansion (GCE)-based bioorthogonal labeling offers an elegant way for direct labeling of proteins in live cells with fluorescent dyes. This labeling approach is currently not broadly used live cell applications, partly because it needs to be adjusted to the specific protein under study. Here, we present a generic, 14-residues long, N-terminal tag for GCE-based labeling of proteins in live mammalian cells. Using this tag, we generated a library of GCE-based organelle markers, demonstrating the applicability of the tag for labeling a plethora of proteins and organelles. Finally, we show that the HA epitope, used as a backbone in our tag, can be substituted with other epitopes and, in some cases, can be completely removed, reducing the tag length to 5 residues. The GCE-tag presented here offers a powerful, easy-to-implement tool for live cell labeling of cellular proteins with small and bright probes.