Comparative studies on membrane-associated, folded chromosomes from Escherichia coli

Nuclear bodies were isolated from Escherichia coli spheroplasts by two different lysis procedures. Their lipid and protein content and the superhelix density was measured. The preparations differed mainly in respect to the amount of the attached membrane material, which seems to be an essential factor in maintaining the stability of the nuclear bodies. The superhelix density was found to be higher than that of naturally occurring, covalently closed, circular deoxyribonucleic acids. The influence of the preparative method on the superhelicity was comparatively small.