[Nature of breaks inducible in DNA at the early stages of interphase cell death].

Dynamics of changes in 3'-OH- and 5'-OH-ends of DNA was determined by "nick"-translation and direct polynucleotide kinase reaction, respectively, in animal thymocytes after irradiation and administration of hydrocortisone. Breaks bearing both 3'-OH- and 5'-OH-ends were found in DNA after irradiation. In 40 min repair of single-strand breaks was almost completed, and enzymatic breaks were accumulated with 3'-OH-ends only. 60 min after the administration of hydrocortisone, the number of nuclear DNA breaks containing 3'-OH-ends, but not 5'-OH-ends, sharply increased. Upon DNA autolysis in isolated nuclei acid nuclease produced 5'-OH-ends, and Ca2+/Mg2+-dependent nuclease, 3'-OH-ends. No activity of Mg2+-dependent nuclease was registered either in the nuclei of control thymocytes or in the nuclei isolated from thymocytes of exposed rats.