paGFP

paGFP, or photoactivatable green fluorescent protein, is a variant of GFP engineered to be non-fluorescent or only weakly fluorescent until it is activated by brief illumination with near-UV or violet light, typically around 405 nm. Once activated, paGFP adopts a bright green fluorescent state that can be excited with blue light (about 488 nm) and emits strongly in the green range roughly around 510–530 nm.

The defining feature of paGFP is spatiotemporal control over fluorescence. By selectively activating a subset of paGFP-tagged molecules within a cell or tissue, researchers can monitor the subsequent movement, diffusion, turnover, or interactions of those labeled molecules over time. Activation is effectively irreversible under standard imaging conditions, allowing persistent tracking of the labeled population.

Common applications include studying protein dynamics, tracking organelles or cytoskeletal components, and performing lineage tracing in developing tissues or intricate cellular contexts. PaGFP is frequently used with conventional fluorescence microscopes such as confocal or wide-field systems for live-cell imaging and can be integrated with quantitative analyses that compare activated pools over time or across regions.

Limitations and considerations include the need for activating light, which can cause phototoxicity if overused; potential background activation; and, relative to some newer fluorophores, moderate brightness and photostability. Experimental design typically requires careful calibration of activation dose, timing, and controls to accurately interpret the behavior of the labeled molecules.