title: [Complexes of histone H1 with supercoiled DNA].
abstract: The action of DNA topoisomerase I on the complexes of supercoiled DNA (DNA I) with histone H1 and other histones was studied at different ionic conditions and histone/DNA ratios. In the presence of 0.15 M NaCl at histone H1/DNA ratios lower than 0.25 (w/w) the relaxation of DNA I is not inhibited. Raising of H1/DNA I ratio up to 0.7 is followed by significant inhibition of DNA I relaxation. At fixed H1/DNA I ratio maximal inhibition is detected at 0.25 M NaCl. At NaCl concentrations lower than 0.1 M and higher than 0.3 M increasing of DNA I relaxation in the presence of H1 was observed. Electron microscopic studies show that increase of ionic strength or H1/DNA I ratio causes more dense packing of DNA molecules in the H1.DNA complexes. Changes in the structure of complexes agree with the increase of DNA I relaxation inhibition in these conditions. DNA I relaxation inhibition by H1 is drastically decreased by iodination of tyrosine 72 residue in the globular part of H1 molecule. Individual core histones inhibit DNA I relaxation at much higher histone/DNA ratios and show different dependence of inhibition on ionic strength. The results are discussed in terms of the possible role of H1 in chromatin condensation-decondensation.
mesh_terms: D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D006657:Histones / Q000378:metabolism*; D007700:Kinetics; D008854:Microscopy, Electron; D009690:Nucleic Acid Conformation; D011485:Protein Binding
chemical_list: D004278:DNA, Superhelical; D006657:Histones; D004264:DNA Topoisomerases, Type I
vernacular_title: Issledovanie kompleksov gistona H1 s superspiral'noĭ DNK.