Live cell imaging with fluorogen activating proteins (FAP). Malachite green (MG), an organic dye and its membrane permeable (MG-Ester) as well as the membrane impermeable variants (MG-11P) are used in FAP imaging. Essentially, the FAP system consists of an encoded protein such as a single chain antibody fragments to activate the fluorescent dye and/or its derivatives. Note, initially MG was used to visualize RNA aptamers. The intracellular trafficking of the membrane bound receptor tyrosine kinase PDGFR is given as an example. Similarly, membrane bound proteins tagged with both FAP and fluorescent proteins like blue fluorescent proteins are useful in studying the protein positioning across the membrane .