High-resolution capillary electrophoretic separation of supercoiled plasmid DNAs and their conformers in dilute hydroxypropylmethyl cellulose solutions containing no intercalating agent.

The three conformers of plasmid pBR322, linear, supercoiled and nicked circular forms, were separated by capillary electrophoresis (CE) in 0.1% hydroxypropylmethyl cellulose (HPMC) solution in the absence of intercalating agents and the migration order was confirmed by co-migration of enzymatically prepared corresponding DNAs. The previously observed broad peaks of supercoiled DNAs in CE are results of unresolved peaks of topoisomers which differ only in the degrees of twisting. We have demonstrated the separation of an artificial topoisomer ladder made from pBR322 and topoisomerase I. The population of topoisomers of a supercoiled DNA is dependent on sample matrices and separation conditions.