Association products and conformations of salt-dissociated and acid-extracted histones. A two-phase procedure for isolating salt-dissociated histones

Abstract

An extremely rapid and efficient method is presented for the separation of salt-dissociated histones from DNA in which the macromolecular components of chicken erythrocyte chromatin are partitioned in a 2-phase system of the water-soluble, nonionic polymers, poly(ethylene glycol) and dextran. The association products and conformations of salt-dissociated histones purified with the 2-phase procedure were compared with histones that had been extracted with 0.4 M H2SO4. In the gel chromatography system of van der Westhuyzen and von Holt, the association products of salt-dissociated and acid-extracted histones are indistinguishable. The circular dichroism (CD) spectra of histones prepared with the 2 methods are identical within experimental error. Histones extracted with sulfuric acid can apparently adopt conformations at least very similar to those of salt-dissociated histones. The CD properties of total erythrocyte histones are the same in 2 M NaCl as those of these histones bound to DNA in chromatin in 1 mM Tris-Cl (pH 7.5). This result and the studies of Weintraub et al. on the patterns of tryptic digest products of histones strongly suggest that in 2 M NaCl the histones exist in conformations very similar to their conformations when bound to DNA. The concept of native histone conformations is discussed in light of these results.