Single pcFP counting in individual bacterial cells by PALM/STORM reveals that a key contributor to the favorable properties of mMaple is a high intracellular concentration of properly folded (and therefore photoconvertible) mMaple fusion proteins.
When the brightness of a large population of cells was assessed by flow cytometry, it was apparent that mMaple-actin or mMaple-actinin was not brighter than either of the corresponding mEos2 or mClavGR2 fusions when expressed in mammalian cells. For the actinin fusion, mClavGR2 had the greatest fraction of bright cells, followed by mMaple and mEos2. For the actin fusion, mClavGR2 and mEos2 had similar distributions that were shifted towards higher brightness relative to mMaple... Although these results were disappointing, we noted that the photostability of mMaple-actin is improved by almost three-fold, increasing the utility of the mMaple-actin construct in applications requiring green-state photostability.