2Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, 117997 Moscow, Russia
* To whom correspondence should be addressed.
Received November 10, 2009; Revision received June 10, 2010
Rat liver nucleus histone H1 was fractionated by polyglutamic acid (PG) in the presence of distamycin A (DM) or chromomycin A3 (CM). In the absence of the antibiotics, PG extracts from the nuclei about half of the nuclear H1. DM or CM added to the nuclei in saturating concentrations weakens the binding potential of most of H1. Titration of nuclei with DM shows that the number of binding sites for DM in the nuclei is less than in isolated DNA by only 20-25%, and this difference disappears after treatment of nuclei with PG. The lower CD value of DM complexes with nuclei compared to that of DM complexes with free DNA is evidence of a change in the DM–DNA binding mode in nuclear chromatin. About 25% of total histone H1 is sensitive only to DM and ~5% is sensitive only to CM. Half of the DM-sensitive H1 fraction seems to have a different binding mode in condensed compared relaxed chromatin. A small part of H1 (~3%) remains tightly bound to the nuclear chromatin independent of the presence of the antibiotics. Subfraction H1A is more DM-sensitive and H1B is more CM-sensitive. UV irradiation of nuclei results in dose-dependent cross-linking of up to 50% of total H1, which is neither acid-extractable nor recovered during SDS electrophoresis. PG with DM extracts only about 3% of H1 from UV-stabilized chromatin. DM treatment of the nuclei before UV irradiation results in extraction of the whole DM-sensitive H1 fraction (~25%), which in this case is not stabilized in the nucleus. A hypothesis on possible roles of the found H1 fractions in chromatin structural organization is discussed.
KEY WORDS: cell nucleus, chromatin, histone H1, polyglutamic acid, distamycin, chromomycin, UV irradiation