Alkaline endonuclease(s) activity in the thymus and spleen of normal and irradiated mice

Evidence has been found on an alkaline endonuclease activity in the cytoplasmic and nuclear fraction isolated from the thymus and spleen mice. The chromatin-associated endonuclease activity was identified only in the spleen. The enzyme(s) was active on both single- and double-stranded DNA, but the reaction was faster if single-stranded DNA was used as a substrate. Maximum activity was found in the pH range of 7.9 to 8.1 in the presence of 10 mM Mg2+ and 1 mM Ca2+. The enzyme(s) splits DNA, yielding 3'-hydroxyl terminated polynucleotides. It is suggested that this alkaline endonuclease(s) is responsible for the formation of deoxyribopolynucleotides in the thymus and spleen of irradiated mice.