DNA from viruses of the papilloma group is circular and supercoiled with a molecular weight of 5.3 million daltons (1). At present little is known of the mechanism by which supercoiling arises or of the biological functions which may be performed by this configuration. To guide speculation on these points it would be desirable to know the sense of the supercoiling turns, whether right- or left-handed, and the number of such turns per molecule of DNA. In the case of polyoma virus DNA, a smaller supercoiled molecule, the interaction of ethidium bromide with the DNA has been used to investigate the twisting of the molecule (2). This communication presents the results of a similar study with DNA from Shope rabbit papilloma virus and human papilloma virus.

Supercoiling appears to result from the number of turns in the Watson-Crick double helix of these circular DNA molecules being either greater or less than the number found in linear DNA of the same size.


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