DNA-Folding by a Stably DNA-Linked Protein in Eukaryotic Chromatin
Higher levels of structural organization of DNA is achieved through its interaction with different proteins. These interactions are abolished by reagents destroying noncovalent associations, hydrogen bonding and S-S bridges. However, in chromatin of different origin a fraction of nonhistone proteins was found whose association with DNA could not be disrupted by such reagents (Lesko and Emery, 1966; Krauth and Werner, 1979; Neuer et al., 1983; Avramova and Tsanev, 1987). The presence of such a protein fraction was proved by in vitro iodination and by in vivo incorporation of labelled aminoacids. This firmly bound protein fraction showed several unusual properties: 1) After iodination it could not enter the Polyacrylamide gels upon electrophoresis. This made impossible the estimation of its molecular mass; 2) The two-dimensional tryptic peptide map of the iodinated protein isolated from eleven different chromatins — Drosophila, fish, frog and rat liver, chicken erythrocytes, rat and ram sperm, Guerin tumor cells, mouse Friend cells, maize leaves and roots — showed a practically identical pattern (Avramova et al., 1989a, b), revealing its high evolutionary conservation; 3) By in vivo labelling of DNA and of the protein it was found that this protein was metabolically stable, transmitted to the progeny like DNA (Avramova et al., 1988a); 4) Chemical and enzymic analysis of the DNA-protein linkage of the stable complex have suggested a bond of a phosphodiester type.
KeywordsProtein Fraction Nuclear Matrix Phosphodiester Bond Sperm Chromatin Chromatin Loop
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