[Electron microscopic study of compactization of individual DNA molecules in films during the interaction with histone H1].

The protein-free method was applied for the investigation of histone H1 DNA complexes formation. The main advantage of this method is the possibility to get intramolecular compact structures at interaction of individual spread molecules of DNA with histone H1. It was shown that in the presence of 0.2-5 micrograms/ml of histone H1 in hypophase there are three types of structures on electronmicroscopic preparations: fibres of non-compacted DNA, compact fibres with twisted strands of duplex DNA and compacted rod-like and circular structures where separate fibres of duplex DNA could not be distinguished. The study of compact structures morphology allows to conclude that they are formed by side-by-side association of DNA fibres, as it takes place in the case of triple rings formation at the compactization of circular DNA due to trivaline binding. At increasing ionic strength there is a tendency for transition from second type structures to the third type structures. The latter can be explained by transition from non-cooperative to cooperative binding of histone H1 to DNA.