Quantitative analysis of the salt-dependent binding behavior of the H2B tail domain

摘要

The core histone tail domains play an essential role in defining higher order chromatin structures and are the sites of post-translational modifications associated with transcription. However, the structures and interactions of the tails and the effect of post-translational modifications, such as acetylation, on these interactions remains poorly defined. Here we introduce a chemical reactivity based assay to assess the binding state of a core histone tail domain. We found that the rates of reactivity of cysteine residues placed within the H2B tail domain were well described by a pre- equilibrium kinetic model. Thus, we were able to determine conformational equilibrium constants describing the distribution of the tail domain between bound and free states over a wide range of salt-conditions. We found that distinct sites within the tail domain exhibited identical salt-dependent behaviors, suggesting a co-operative structure within the bound tail. Analyses of tails containing mutations modeling acetylation indicate that this modification does not cause a global weakening of tail-DNA interactions but rather induces specific and localized structural changes within the tail domain.