[Histone competition for DNA and its possible role in the self-assembly of eu- and heterochromatin]

Electrophoretic analysis of histones bound to DNA and remaining free in the mixtures of DNA with the total histone of chromatin in a medium of physiological ionic strength has shown that even the minimal weight excess of the total histone with reference to DNA (1.1:1) leads to the formation of nucleohistone impoverished in HI fraction because of histone competition for DNA. Within the histone/DNA ratio equal to 1.4, H3, H4, H2A and H2B are bound to DNA without competition, i.e. at a ratio in which they are added to DNA. Provided the histone/DNA ratio is higher in the mixture, there form nucleohistones enriched with H3 and H4 fractions. The role of histone competition for DNA in eu- and heterochromatin assembly is discussed.