  We construct and analyze monomeric and multimeric models of the stochastic
disassembly of a single nucleosome. Our monomeric model predicts the time
needed for a number of histone-DNA contacts to spontaneously break, leading to
dissociation of a non-fragmented histone from DNA. The dissociation process can
be facilitated by DNA binding proteins or processing molecular motors that
compete with histones for histone-DNA contact sites. Eigenvalue analysis of the
corresponding master equation allows us to evaluate histone detachment times
under both spontaneous detachment and protein-facilitated processes. We find
that competitive DNA binding of remodeling proteins can significantly reduce
the typical detachment time but only if these remodelers have DNA-binding
affinities comparable to those of histone-DNA contact sites. In the presence of
processive motors, the histone detachment rate is shown to be proportional to
the product of the histone single-bond dissociation constant and the speed of
motor protein procession. Our simple intact-histone model is then extended to
allow for multimeric nucleosome kinetics that reveal additional pathways of
disassembly. In addition to a dependence of complete disassembly times on
subunit-DNA contact energies, we show how histone subunit concentrations in
bulk solution can mediate the disassembly process by rescuing partially
disassembled nucleosomes. Moreover, our kinetic model predicts that remodeler
binding can also bias certain pathways of nucleosome disassembly, with higher
remodeler binding rates favoring intact-histone detachment.
