[DNA distribution in fractions differing in the strength of association with nuclear matrix during activation of DNA endonucleases in cell nuclei and treatment with nuclease S1].

Influence of activation of Ca2+/Mg2(+)-dependent, Mn2(+)-dependent, Mg2(+)-dependent and acidic endogenous DNAses on distribution of DNA in fractions differing in tightness of association with the nuclear matrix has been investigated. In the intact cell nuclei all types of DNA-protein bonds were obscured by a tight bonding of DNA with the proteins of replicative complex. Activation of endogenous nuclease activities caused detachment of a significant chromatin fraction from the nuclear matrix, fraction of DNA remained attached to the replicative complex, small fraction of DNA was bound to the nuclear matrix with a less tight bond. The endogenous nucleases are supposed to make cuts mainly in distal parts of the chromatin loops and do not affect the replicative complex, where the tight DNA-matrix bond is localized. Single-strand DNA-specific S1-nuclease preferably attacks the latter site.