ORGANIZATION OF MAMMALIAN CHROMOSOMAL DNA - SUPERCOILED AND FOLDED CIRCULAR DNA SUBUNITS FROM INTERPHASE CELL-NUCLEI

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  • 1 January 1978
    • journal article
    • research article
    • Vol. 37  (3) , 421-432
Abstract
Chinese hamster lung cells (line V79/4) in the G2 phase of the mitotic cycle were lysed on neutral sucrose gradients. The released chromosomal DNA was characterized according to size and shape by sedimentation velocity studies. Using the intercalating agent, ethidium bromide in the gradients and the induction of DNA single- and double-strand breaks by irradiation, the DNA was released into the gradient in supercoiled circular subunits whose homogenous size corresponds to 2.8 .cntdot. dalton. Supercoiling of these DNA subunits was confined to smaller regions sized on the average about 9 .cntdot. 107 dalton and maintained by folding the DNA in loops. The average superhelix density was -0.09 turns/10 base pairs of DNA. The functional aspects of the experimental findings are discussed in terms of replicative and transcriptional units.