title: Molecular motion of DNA as measured by triplet anisotropy decay.
abstract: We have used triplet anisotropy decay techniques to measure the internal flexibility and overall rotational motion of DNA, covering a time range from 15 ns to 200 mus. Nearly monodisperse DNA fragments 65--600 base pairs long were studied by using the intercalating dye methylene blue as a triplet probe. We found that the slow end-over-end tumbling of short DNA fragments (less than or equal to 165 base pairs) is as predicted for a rigid rod. As expected, a longer DNA fragment (600 base pairs) experiences slow segmental motion of its helix axis. We found that, at the earliest times, anisotropy decays more rapidly than expected for a rigid rod, suggesting that, when bound, methylene blue monitors fast internal motion of the helix. Since the rod-like end-over-end tumbling of short fragments rules out fast bending motions, we conclude that the fast components of DNA anisotropy decay are due to twisting motion of the helix, occurring with a time constant near 50 ns.
mesh_terms: D004247:DNA; D007364:Intercalating Agents; D007700:Kinetics; D008751:Methylene Blue; D008970:Molecular Weight; D009038:Motion; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D007364:Intercalating Agents; D004247:DNA; D008751:Methylene Blue