Feng, S. et al. Nat Commun. 8, 370 (2017).

Split fluorescent proteins are used for a variety of purposes, including protein labeling and bimolecular fluorescence complementation assays that probe whether proteins of interest are in close proximity. Split fluorescent proteins are typically composed of two separately expressed fragments of a circularly permuted version of a fluorescent protein that come together to form an intact fluorescent protein. Feng et al. have developed improved split fluorescent proteins based on mNeonGreen and mCherry. Compared with a commonly used split GFP, split-mNeonGreen21–10/11 has an improved ratio of complemented signal to background. Compared with split-sfCherry2, split-sfCherry21–10/11 shows ten-fold higher brightness. The researchers also developed a photoswitchable form of split-sfCherry21–10/11 that enables super-resolution imaging of split fluorescent proteins. They demonstrate the power of these tools to study the abundance of Sec61B in different parts of the endoplasmic reticulum.