Organizational changes in chromatin at different malignant stages of Friend erythroleukemia

Abstract

The chromatin structure of morphologically-similar, but increasinglymalignant erythroleukemia cells was investigated using mild micrococcal nuclease digestion of isolated nuclei. The maximum solubilization of chromatin was unique for each of the three cell types: the least malignant (our (190 bp). In addition, while the DNA of mononucleosomes depleted in Hi was smaller than that in the Hicontaining species, relative size differences among the different cell types were retained. These data suggested that the difference in the mononucleosome particle size resistant to nuclease digestion was independent of histone Hi. Differences in nucleosome repeat length were also noted among the cell types. These studies have demonstrated dramatic differences in chromatin structure associated with malignant potential of an otherwise morphologically identical cell type. These findings may reflect changes in the relative amounts of H2a variants which we have previously described among the different malignant cell types.

Induction of a Ca2+, Mg2+-dependent endonuclease activity during the early stages of murine erythroleukemic cell differentiation.

“…The increased sensitivity of these cells to x-ray damage may be related to the level of DNA breakage and/or endonucleolytic repair capacity of the cell. In addition, the transient appearance of endonuclease activity in the cultured Friend cell may reflect a tightly regulated activity of the endonuclease in relation to a particular aspect of the cell cycle, because the time of appearance of endonuclease activity correlates with a period of G1 arrest (23,31). This is important, because cells have been shown to accumulate DNA strand breaks during G1 arrest (32).…”