Gamma irradiation or hydrocortisone treatment of rats increases the proteinase activity associated with histones of thymus nuclei.

An increase in the activity of histone-associated rat thymus nucleus proteinases specific for histones H2A, H2B and H1 was shown after gamma irradiation or hydrocortisone treatment of animals. Histone H1-specific proteinase activity is dependent on DNA and increases in the presence of denatured DNA, whereas proteinases specific for core histones are inhibited in the presence of denatured DNA. The increase in the activity of histone-associated proteinases depends on the radiation dose and the time after irradiation or hydrocortisone injection. In the presence of dithiotreitol and sodium dodecyl sulfate, these proteinases dissociate from histones. It was found by gel electrophoresis that several proteinases of various molecular masses are closely associated with histones obtained from thymus nuclei of irradiated or hydrocortisone-treated rats.