Metaphase chromosome and nucleoid differences between CHO-K1 and its radiosensitive derivative xrs-5

Jeffrey L. Schwartz, Janet M. Cowen, Erich Moan, B. A. Sedita, Janet Stephens, Andrew T M Vaughan

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


The Chinese hamster ovary (CHO) cell line xrs-5 is a radiation-sensitive mutant isolated from CHO-K1 cells. The radiation sensitivity is associated with a defect in DNA doublestrand break rejoining. Chromatin structure also appears altered in xrs-5 cells compared with the parental CHO-K1 cells. Metaphase chromosomes from xrs-5 are more condensed in appearance than CHO-K1 chromosomes. The overcondensed look is not the result of colcemid sensitivity. Electron microscopy studies suggest that xrs-5 metaphase chromosomes have larger loops of chromatin extending out from the chromosome core. There are also differences between CHO-K1 and xrs-5 cells in the size and fluorescence pattern of ethidium bromide-stained nucleoid preparations. These results suggest that there is a fundamental difference between CHO-K1 and xrs-5 in either the organization of the supercoiled loops of DNA attached to the nuclear matrix or in the nature of the proteins that attach the DNA to the matrix. These alterations in chromosome structure may underlie, in part, the radiation sensitivity of xrs-5 cells.

Original languageEnglish (US)
Pages (from-to)105-108
Number of pages4
Issue number2
StatePublished - Mar 1993
Externally publishedYes

ASJC Scopus subject areas

  • Statistics, Probability and Uncertainty
  • Applied Mathematics
  • Health, Toxicology and Mutagenesis
  • Toxicology
  • Genetics(clinical)
  • Genetics


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