Isolated mammalian metaphase chromosomes. I. General characteristics of nucleic acids and proteins

The metaphase chromosomes of tissue culture cells derived from four different mammalian species have been isolated in relatively large quantities at neutral pH and essentially free of nuclei and microscopically visible cytoplasmic debris. Some characteristics of the nucleic acids and proteins associated with these chromosome preparations are given below. The average chemical composition of the HeLa chromosome preparations is 16% DNA, 12% RNA and 72%, protein. Similar chemical compositions are reported for the chromosomes from Syrian and Chinese hamster cells and mouse L-cells. The DNA and RNA associated with the HeLa chromosomes have G + C contents of 41 and 63%, respectively. The DNA from the isolated metaphase chromosomes of the four cell types studied here exhibits the same density and very similar band profiles in CsCl density-gradient centrifugation as DNA extracted directly from the interphase nuclei of the respective cells. The satellite band of mouse L-cell DNA is present in chromosomal DNA in the same proportion as in DNA from interphase nuclei. More than 80% of the RNA associated with the HeLa chromosome preparations is 28 s and 16 s in the proportion of 2:1. At least 50% of the chromosomal protein is acid-soluble and shows an acrylamide gel electropherogram similar to that of acid-soluble proteins extracted from the nuclei of the respective cells.