||Li G, Levitus M, Bustamante C, Widom J. Rapid spontaneous accessibility of nucleosomal DNA. Nat Struct Mol Biol. 2005 Jan12(1):46-53.PubMed ID15580276
||Studies using fluorescence resonance energy transfer (FRET) reveal that site exposure involves large increases in separation between a fluorescence donor on one end of the nucleosomal DNA and a fluorescence acceptor on the histone core, implying that site exposure occurs by progressive unwrapping of the nucleosomal DNA starting from one end of the nucleosome. A second approach is based on fluorescence correlation spectroscopy (FCS) of small numbers of nucleosomes at a time, diffusing freely in dilute solution.
||The opening rate constant (k12) of approximately 4 s-1 corresponds to a lifetime in the fully wrapped state (tau wrapped) = 1/k12 250 ms. Nucleosomes in solution look like those imaged by crystallography only for very short periods of time, < <1 s, before undergoing a large-scale spontaneous unwrapping event.