An endonuclease activity of chicken erythrocyte nuclei and mononucleosomes

Endogenous nuclease is present in the nuclear sap of chicken erythrocyte nuclei. This enzyme resembles the nuclease of mammalian nuclei in requirements for bivalent cations and in production of large chromatin fragments that gradually decrease in size, but differs in that the products do not go through the stage of discrete bands on gel electrophoresis. Endogenous nuclease and micrococcal nuclease are also detectable in mononucleosomes prepared from chicken erythrocytes with the aid of micrococcal nuclease. Both nucleases are extractable with 0.35 M NaCl, and both are inhibited by pTp. In the absence of Ca2+, the micrococcal nuclease is totally inactive, whereas the endogenous nuclease shows a low level of activity.