The molecular basis of several genetically targetable fluorescent tags amenable to live cell imaging is explored and development and use of fluorescent biosensors for studying dynamic signaling processes in living cells is discussed. The green fluorescent protein (GFP) from the jellyfish Aequorea victoria are found to generate their chromophores autocatalytically by post-translational modification of their primary amino acid sequence. Studies have found that wild-type A. victoria GFP generates a highly fluorescent p-hydroxybenzylidene-5-imidizolinone (p-HBI) species from the tripeptide, Ser65-Tyr66- Gly67. Kamiyama and Chiba used a FRET-based activation reporter, termed A-probe.1, to measure the endogenous activation patterns of the Rho GTPase, Cdc42, during Drosophila embryogenesis. With continued advances in biosensor development, the quality and depth of information that can be incorporated into models of signal transduction will continue to increase, promoting a more quantitative understanding of the molecular mechanisms that influence signaling dynamics inside the cell.
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