DOI: 10.1073/pnas.62.4.1159 ISSN:

SUPERCOILED CIRCULAR DNA-PROTEIN COMPLEX IN Escherichia coli : PURIFICATION AND INDUCED CONVERSION TO AN OPEN CIRCULAR DNA FORM

Don B. Clewell, Donald R. Helinski
  • Multidisciplinary

The 23 S twisted circular form of Col E 1 DNA has been isolated from Escherichia coli as a tightly associated DNA-protein complex with a sedimentation coefficient of approximately 24 S . Treatment of this complex with pronase, trypsin, sodium dodecyl sulfate, Sarkosyl, or heat results in a conversion to a slower sedimenting form of 17 S or 18 S , as determined by centrifugation in neutral sucrose gradients. These treatments do not alter the sedimentation properties of noncomplexes supercoiled Col E 1 DNA even in the presence of the Col E 1 -protein complex. Electron microscopic analyses indicate that the decrease in sedimentation rate of the Col E 1 -protein complex after treatment with these various agents is largely owing to an induced transition of Col E 1 DNA from the supercoiled to the open circular state.

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