We report the development and application of photoactivatable Green Cherry 
(G(PA)C), the first genetically encoded "continuously red-photoactivatable 
green" two-color probe for live cell imaging. G(PA)C is unique in that it 
enables real-time tracking of selected subpopulations of proteins and organelles 
in the cell or of cells within tissues and whole organisms, with constant 
reference to the entire population of the probe. Using G(PA)C-zyxin as proof of 
utility, we obtained new insights into the dynamic movement of the cytoskeletal 
protein zyxin. We show that zyxin is continuously and rapidly recruited from the 
cytosol into established focal adhesions. It can also move rapidly within a 
given focal adhesion and "hop" between adjacent focal adhesions, emphasizing the 
dynamic nature of proteins within these structures. The in vivo utility of 
G(PA)C is exemplified by tracking hemocyte movements using a versatile 
transgenic Drosophila model engineered to express G(PA)C in tissues and cells of 
interest under the control of the GAL4-inducible promoter.