BIOCHEMICAL EVIDENCE OF VARIABILITY IN DNA REPEAT LENGTH IN CHROMATIN OF HIGHER EUKARYOTES (CHROMATIN STRUCTURE-NUCLEOSOME-MICROCOCCAL NUCLEASE)

Biochemical evidence is presented which confirms that the DNA repeat length in micrococcal nuclease (spleen endonuclease, nucleate 3''-oligonucleotidohydrolase, EC 3.1.4.7) digests of Chinese hamster ovary chromatin is shorter than that of rat liver chromatin. A survey of available cells has shown that the DNA repeat length of the chromatin of higher eukaryotes varies widely. A value of 196 base pairs was found for cells of all mature tissues, regardless of the source of the tissue, whereas smaller values were found for cells of actively dividing tissues and larger values were found for a genetically inactive cell. Although the DNA repeat length of the chromatin of cells in culture was usually shorter than 196 base pairs, there was no general correlation between the size of the chromatin DNA repeat length and the rate of cell division or the functional state of the cell in culture. Examination of extensive micrococcal nuclease digest suggests that the chromatin subunits of all of the higher eukaryotic cells studies contain a core with approximately 140 base pairs of DNA.