Hyperpolymer formation during renaturation of DNA from genomes with different sequence organisation

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Abstract
Hyperpolymer formation during the renaturation of DNAs from wheat, calf and E. coli was studied using hydroxyapatite chromatography, electron microscopy and s1 nuclease. Large hyperpolymers could not be eluted from hydroxyapatite with 0.5 M phosphate buffer at 60°C. Large proportions of wheat and E. coli DNAs were incorporated into hyperpolymers when fragments 650 nucleotides long were renatured. A much smaller proportion of calf DNA was incorporated under equivalent conditions. Greater proportions of calf DNA accumulated in hyperpolymers only when longer fragments were incubated. Electron microscopy indicated no obvious differences in the basic structures of hyperpolymers formed by the three DNAs and confirmed the quantitative differences in hyperpolymer formation found by hydroxyapatite chromatography. It is concluded that the proportions and arrangement of the repeated sequences in the chromosomes of higher organisms determine the extent of rapid hyperpolymer formation during DNA renaturation in vitro.

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