[Features of structural organization of chromatin from various sources]

The conformational peculiarities of DNA and histones of chromatins of different origin have been studied using circular dichroism (CD). The chromatins were isolated from pigeon brain, rat thymus and liver, ascitic hepatoma 22A, C3HA mouse liver, pigeon erythrocytes and sea urchin sperm. The functional peculiarities of the chromatins were found to correlate with their compactness and the nucleosomal DNA repeat length. Analysis of chromatin CD spectra made it possible to define the degree of DNA compactness in oligonucleosomes and the secondary structure of their linker histones of the H1 family. It was found that in low ionic strength solutions the structures of chromatosomes are formed in erythrocyte and thymus chromatins, but not in sea urchin sperm chromatin. The size of the compact part of the DNA in the nucleosomes of transcriptionally active chromatins of brain and ascitic hepatoma 22A are less than the length of the DNA of the core particles under identical conditions. The secondary structure of the H1 histone from sea urchin sperm chromatin, unlike other linker histones of the H1 family, contains an additional alpha-helical segment in the C-terminal part. Analysis of structural changes of the both chromatin components during condensation of their oligonucleosomal chains with an increase in the ionic strength has been carried out.