Topological alteration of plasmid DNA during cell growth of Escherichia coli

Superhelical alteration of plasmid DNA in Escherichia coli cells was observed during cell growth. Plasmid DNAs were being supercoiled while the cells were actively dividing, and they were partially relaxed after the cultures reached stationary. Unknown structural materials of plasmid DNA which migrated faster than usual superhelices in agarose gel electrophoresis were found among the strains regardless of gyrase genotype.