Nucleoproteins of Cell Nuclei

We have prepared nucleoproteins from a wide variety of animal cells- from mammalian liver, kidney, pancreas, spleen, thymus, brain, from the liver, spleen and blood cells of the dogfish, and from the sperm of the trout, shad, frog and sea urchin.These nucleoproteins are located in the nuclei of the cells from which they are derived.In this paper we shall briefly de- scribe the method of preparation, some properties of the nucleoproteins and the evidence that they are in fact derived from cell nuclei.I. Preparation.-Toextract these nucleoproteins from the cell and to separate them from other cellular constituents nothing more drastic is used than neutral sodium chloride solutions of varying concentrations.Before extraction, much cytoplasmic material is removed by thoroughly washing the minced tissue with physiological saline.From liver more than 60 per cent of all the protein present can be removed in this manner with- out destroying the main outlines of cell structure.The washed tissue is then extracted with 1 M NaCl (2 M NaCl is needed for extraction of sea- urchin sperm).As soon as the more concentrated salt solution is added the mixture becomes exceedingly viscous.By centrifugation at high speed (10,000 to 12,000 r. p. m.) a viscous, slightly opalescent supernatant fluid is obtained.The supernatant fluid is viscous because of the nucleoprotein dissolved in it.When this solution is added to six volumes of water the nucleoprotein precipitates in a fibrous mass, settling rapidly so that the supernatant fluid can be syphoned off.The precipitate is washed with 0.14 M NaCl and then redissolved in 1 M NaCl.The solution is centrifuged at high speed to remove any suspended material.The nucleoprotein is reprecipitated by pouring into six volumes of water.If the mixture is stirred with a rod having a crook at its end, the fibrous material generally winds around the rod and adheres to it when the rod is transferred to another vessel (Plate I).The nucleoprotein is again dissolved, centrifuged and precipitated.At this point the preparation is frequently considered to be finished, although purification can be carried further.For further purification advantage is taken of the unusual solubility of the nucleoprotein.It is soluble in 1 M NaCl, insoluble in 0.14 M NaCl and soluble again when the salt concentration is reduced to approximately 0.02 M. When a solution of nucleoprotein in 1 M NaCl is placed in a cellophane tube and dialyzed against water the nucleoprotein first precip- itates and then tends to redissolve as the salt concentration within the