Simian virus 40 DNA extracted from infected cells with sodium deoxycholate no longer reflects its in vivo superhelix density.

When simian virus 40 DNA is extracted from infected cells with low concentrations of sodium deoxycholate, which selectively extract non-encapsidated simian virus 40 DNA, the DNA has a lower average number of superhelical turns than the DNA extracted from purified viral particles. During extraction, a partial deproteinization of the DNA by a concentration of detergent that did not inactivate a nicking-closing activity led to the removal of some superhelical turns. The DNA extracted in this way no longer reflected its in vivo number of superhelical turns.