[Chromatin degradation in the death of thymic lymphocytes induced by radiation or dexamethasone: the necessity for a stage of preliminary proteolysis].

Proteolytic activity in a protein fraction of a rat thymocyte nuclear matrix was found to increase 1-2 h after gamma-irradiation or administration of dexamethazone. Cycloheximide did not prevent the observed protease activation. Neither histons nor thymocyte nuclear matrix proteins were subjected to proteolysis after exposure to radiation or the hormone. Such proteolysis inhibitors as phenylmethylsulfonyl fluorine, trasilol, and partly leupeptine inhibited nuclear DNA degradation in irradiated and dexamethazone treated thymus lymphocytes. In all appearance, this effect was not due to Ca/Mg-dependent endonuclease inactivation. The same was observed in the system of autolytic chromatin degradation in isolated thymocyte nuclei.