FUNCTIONAL-ORGANIZATION OF PLANT NUCLEAR-DNA .2. BEHAVIOR OF DNA TOPOII COMPLEX IN ISOLATED-NUCLEI

The properties of the topoisomerase II-DNA complex in nuclear preparations were investigated. The complex was found to function similarly in Mg2+- and Ca2+-containing media. Unlike the in vitro assay, treatment of topoII-DNA complex with EDTA enhanced nuclear DNA cleavage rather than its rejoining. The topoII-DNA complex treated with SDS was found to acquire the capacity of subsequent SDS-independent nuclear DNA cleavage. The salient features of DNA-topoII complex are supposed to be due to the enzyme involvement in formation of high-order chromatin structure leading to initial stabilization of the complex in vivo. It was supposed that cells harbor different topoII-DNA complex variants of possible physiological significance.