Micro-environment of the H3-H3 contact region of a nucleosome core particle, as revealed by a lifetime measurement of a fluorescent probe.

A sample of fluorescently-labeled nucleosome core particles was prepared by combining N-(3-pyrene)-maleimide to each of the two cysteine residues of the two H3 histones in the chicken erythrocyte nucleosome core particle, by a method previously reported by Zama et al. (Nucl. Acids Res. 5, 3881 (1978)). The fluorescence spectra and fluorescence lifetime of the sample in solvents with various Na+ concentrations have been examined. Three different types of micro-environment of the fluorescent probe have been found: (i) emits a pyrene dimer fluorescence at 460 nm, (ii) emits a pyrene monomer fluorescence with a long (75-65 ns) lifetime, and (iii) emits a pyrene monomer fluorescence with a short (5-15 ns) lifetime. The manner of dislocation of the two H3 subunits from each other in each of the solutions with different salt concentrations was discussed.