FRET Experimental Design (IMAGE) Arizona State University Caption Fluorescence resonance energy transfer (FRET): experimental design. Nucleosomes are constructed having a fluorescent donor (cyan) attached to one end of the DNA, and a fluorescent acceptor (magenta) attached nearby on the histone protein core. In the middle diagram, spontaneous partial unwrapping of the DNA thread exposes a hidden DNA target site (hatched area), which is site-specific for the DNA binding protein LexA. When LexA is added in sufficient concentration, nucleosomes are temporarily trapped in their unwrapped state. The distance between the two fluorescent molecules changes as the DNA unwraps and rewraps, allowing the process to be precisely measured. Credit Reprinted from: <I>Journal of Molecular Biology</I>, volume 411(2), Tims HS, Gurunathan K, Levitus M, Widom J, Dynamics of nucleosome invasion by DNA binding proteins, pgs 430-48, with permission from Elsevier. Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.