Biopolymers and cell. 1985. Volume 1. № 1. 32 - 40
V. V. Terskikh, I. B. Bronstein, I. I. Gromova, A. V. Timofcev, K. A. Kafiani
DNA-TOPOISOMERASES OF PROLIFERATING ANIMAL CELLS
Summary
Chinese hamster fibroblasts were stimulated to proliferate by adding 10 % embryonic serum to the culture. Specific activity of type 1 topoisomerase in partially purified nuclear extracts, prepared at various times after serum addition, markedly increased, peaking at the 10th hour, 10 hour before a mass entry of the cells into the S-phase. This indicates a role of topoisomerase I in the control of cell proliferation. With the aim of developing an approach to isolation and analysis DNA sequences that are the targets for topoisomerases in the cell, complex formation between the highly purified topoisomerase I and circular supertwisted DNA (of the plasmid pBR322) or nuclear DNA of Chinese hamster fibroblasts was studied. Isolation and characterization of the complexes by sedimentation and equilibrium density centrifugation are described, which allows characterizing the protein as well as the DNA moieties of the complexes.