title: Interaction of histone H1 with superhelical DNA. Sedimentation and electron microscopical studies at low salt concentration.
abstract: Complexes of histones H1 with superhelical SV40 DNA obtained by direct mixing were studied in 0.1 SSC buffer corresponding to 0.02 M Na+. Depending on the molar input ratio H1/DNA three classes of sedimenting species were observed: (1) a component sedimenting similar to superhelical DNA with a sedimentation coefficient s2o,w of 25 S observable up to 335 Mol H1/Mol DNA (w/w = 2); (2) a component with s2o,w = 120 S appearing at 135 Mol H1/Mol DNA and (3) growing amounts of heterogeneous aggregates greater than 1000 S. Electron micrographs revealed the 25 S component to consist of double-fibers formed from one DNA molecule and the 120 S component to consist of bundles of several such double-fibers. The aggregates represent cable-like structures. The addition of ethidium bromide to 25 S complexes induces the formation of bundles, if H1 is present in a quantity which alone is not sufficient to bring about this effect. This result indicates that ethidium bromide effects a redistribution of H1 molecules and that H1 is responsible for the bundle formation.
mesh_terms: D004278:DNA, Superhelical / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D007700:Kinetics; D008854:Microscopy, Electron; D009994:Osmolar Concentration; D011485:Protein Binding; D013539:Simian virus 40
chemical_list: D004278:DNA, Superhelical; D004279:DNA, Viral; D006657:Histones