SCN(-) binding to the charged lysines of histones end domains mimics acetylation and shows the major histone-DNA interactions involved in eu and heterochromatin stabilization

SCN- binds to the charged amino group of lysines, inducing local changes in the electrostatic free energy of hi stones. We exploited this property to selectively perturb the histone-DNA interactions involved in the stabilization of eu and heterochromatin. Differential scanning calorimetry (DSC) was used as leading technique in combination with trypsin digestion that selectively cleaves the histone end domains. Euchromatin undergoes progressive destabilization with increasing KSCN concentration from 0 to 0.3 M. Trypsin digestion in the presence of 0.2 M KSCN show that the stability of the linker decreases as a consequence of the competitive binding of SCN- to the amino groups located in the C and N-terminal domain of H1 and H3, respectively; likewise, the release of the N-terminal domain of H4 induces an appreciable depression in both the temperature and enthalpy of melting of core particle DNA. Unfolding of heterochromatin requires, in addition to further cleavage of H4, extensive digestion of H2A and H2B, strongly suggesting that these histones stabilize the higher order structure by forming a protein network which extends throughout the heterochromatin domain.