The authors tested the novel fluorescent protein in HEK 293 mammalian cells using a tetracycline-inducible expression system, in Caenorhabditis elegans embryos using heat shock-regulated expression, and in Xenopus laevis to test Otx-2-regulated expression. In all cases when promoters were recently turned on, the cells fluoresced green. When they stopped expressing, the cells fluoresced red after three hours. And in cases of continuous expression, the mixing of green and red produced a yellow hue. The researchers reported that in the C. elegans experiments the red-to-green ratio changed linearly within the first 14 hours, giving a new measurement for time elapsed after heat shock. By measuring the green-to-red ratio one can determine the point at which a promoter was turned off. It provides, the authors said, "an easy and reliable way to analyze the 'history' of gene expression and gives the ability to monitor two equally important processes: activation and down-regulation of ...
Green Light, Red Light
Screening random mutations of the red fluorescent protein drFP583 from tropical coral, researchers at the National Institutes of Health, Stanford University School of Medicine, the Institute of Bioorganic Chemistry at the Russian Academy of Science, and Palo Alto, Calif.-based BD Biosciences-CLONTECH made an unusual discovery.1 After fluorescing green for about three hours, a mutant protein called E5 matures and begins to fluoresce red; thus, E5 acts like a stopwatch, telling researchers when th
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