Low-speed purification of human placental nuclei

A simple method for the purification of human placental nuclei is described. Nuclei were isolated by homogenizing tissue in standard saline citrate solution in the presence of zinc chloride to stabilize the nuclear membranes, NP40 as non-ionic detergent and sodium bisulphite for inhibition of proteolytic activity. Nuclei purification was achieved by low-speed centrifugation through a discontinuous sucrose gradient. The purified nuclei were evaluated by morphological criteria using phase contrast and electron microscopy. The extent of contamination by cytoplasmic debris was estimated by Papanicolaou's staining technique. Biochemical criteria include measurements of alkaline phosphatase activity as a plasma membrane enzyme marker and DNA-dependent RNA polymerase activity for the functional integrity of nuclear components. Transcriptionally active nuclei were obtained but the yield of nuclei was low; however, this low yield is compensated by the high degree of purity, the simplicity of the method and the functional and morphological integrity of the purified nuclei.