Determination of some nuclear deoxyribonucleases in X-irradiated rat thymocytes

Summary The spectrum of nuclear nucleases in control and irradiated (4 Gy) thymocytes has been investigated. Using the method of SDS electrophoresis of nuclear proteins in³H - DNA-polyacrylamide gels a number of polypeptides of MW. 35, 32, 17.7, 17.2 and 16.4 kDa possessing nuclease activity were found. The 35 kDa enzyme is only active in the presence of Ca²⁺ and Mg²⁺ ions. In response to cycloheximide injection (3 mg/100 g body weight) and irradiation, we did not detect the 35 kDa nuclease activity. Nucleases of 32, 17.7, 17.2 and 16.4 kDa are active in the presence of Ca²⁺ ions. The activities of these nucleases increases 60 min after irradiation. These nucleases were also found in the fraction of polydeoxyribonucleotide (PDN).