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Published March 1969 | Published
Journal Article Open

The use of an ethidium analogue in the dye-buoyant density procedure for the isolation of closed circular DNA: The variation of the superhelix density of mitochondrial DNA


The separation between open and closed circular DNA in buoyant CsCl gradients containing intercalating dyes depends on the superhelix density of the closed form. These separations are about 1.8 times larger with propidium iodide than with ethidium bromide. The superhelix densities of mitochondrial DNA from HeLa cells and Lytechinus pictus eggs appear to be about two thirds that of mitochondrial DNA from rat and rabbit liver.

Additional Information

© 1969 by the National Academy of Sciences. Read before the Academy October 29, 1968. It is a pleasure to thank T.I. Watkins and Boots Pure Drug Co., Ltd., for providing the ethidium analogues and the 3,8-dinitro-6-phenylphenanthridine, and L. Pikó for supplying the L. pictus M-DNA. We thank L. Wenzel and J. Edens for assistance in the culture of HeLa cells and J. Ceasar for assistance in the preparation of the manuscript. We also wish to thank Professor J. Hurwitz for generously providing advice and facilities to one of the authors (W.B.U.), who prepared the polynucleotide ligase while a guest at Albert Einstein Medical College, Bronx, New York. This work was supported by grants GM 15327-09 and CA 08014-04 from the U.S. Public Health Service and by fellowships (to B.H.) from the National Science Foundation and (to W.U.) from the U.S. Public Health Service. This is contribution no. 3743 from the Division of Chemistry, California Institute of Technology, Pasadena, California.

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October 23, 2023