[Structure of the nucleosome chain. I. Role of histone H1 in oligonucleosome compaction]

The method of sedimentation velocity has been used to study the changes of the oligonucleosome compact state under the influence of various NaCl concentrations and to investigate the role of histone H1 in compaction of nucleosomes. Analysis of dependencies of the sedimentation coefficients on the number of nucleosomes in the chain has demonstrated that histone H1 stabilizes the compact structure of oligonucleosomes in the solution of low ionic strength (mu = 0.01). Removal of histone H1 leads to partial unfolding of the chains of oligonucleosomes. In 0.15 M NaCl solution H1-depleted oligonucleosomes are folded into the compact structure, which is similar to that of oligonucleosomes with histone H1 in solutions of low ionic strength. Further compaction of H1-containing oligonucleosomes in 0.15 M NaCl solution leads to formation of supercoiled structure, stabilized by cooperative interaction of at least five nucleosomes.