The purification of cell nuclei from calf uterus by zonal centrifugation in reorienting density gradients

A method is described for isolation of substantial amounts of pure and enzymatically active nuclei from whole calf uterus. The technique involves a multistep sequential homogenization of the tissue and a zonal centrifugation of the crude nuclear preparation in a reorienting density gradient rotor. Electron and phase contrast microscopic observations show that the nuclei are intact and practically free from cytoplasmic contamination. Based on DNA recovery, the purified fraction contains 9% of the nuclei of the total tissue and more than 19% of the filtered homogenate. The pure nuclear fraction consists of 29% DNA, 7% RNA, and 64% protein, which parallels the composition of purified nuclei from other mammalian tissues.