| Abstract: | The kinetics of a conformational change which occurs in nucleosome core particles at about 1 mM ionic strength have been studied by observing changes in the fluorescence of labeled histone H3. The unfolding reaction is intramolecular since no concentration dependence is observed. However, the kinetics are unexpectedly complicated and reveal evidence of at least three relaxation times. It is possible to fit the kinetics observed under several conditions to a consistent four-state cyclic mechanism in which folded and unfolded forms can inter-convert by two parallel pathways, each involving a distinct intermediate. While the data are not sufficient to establish this mechanism as a unique choice, they exclude many simpler possibilities. The cyclic mechanism is quite reasonable in view of what is currently known about the structures of the folded and unfolded forms. |
