[Dinucleosome as a product of initial chromatin cleavage by endogenous nucleases]

The ability of nucleic endonucleases to recognize dinucleosomal level of chromatin structure was studied. Rat liver chromatin endonucleases were shown to be capable of DNA cleavage at dinucleosome linkers. The cleavage was observed mainly at initial stages of chromatin autohydrolysis, i.e. up to 10-20th min of incubation in the medium containing 5 mmol of magnesium chloride and 2 mmol of calcium chloride. Thus, mononucleosomal DNA in dinucleosomes and other even chromatin subunits was larger and more homogeneous than in odd subunits. The cleavage of autodigested chromatin by bovine spleen and snake venom exonucleases and by nuclease S1 has shown that dinucleosomal structure is independent of differences in the length of internal and external dinucleosome linkers. The initial endonucleolysis appears to be characterized by different accessibility of the linkers for chromatin nucleases.