[Density gradient ultracentrifugation method of studying sibiromycin interaction with linear and circular DNA]

Sibiromycin added to linear chromosomal E. coli DNA in vitro leads to the decrease of bouyant density in neutral CsCl density gradient. This decrease is a linear function of sibiromycin/DNA ratio and amounts to about 32 mg/ml at the ratio equal to 0.1. Binding sibiromycin does not change the degree of hydration of DNA as revealed by centrifugation in metrizamide density gradients. When added to the covalently closed or open circular DNA of PM-2 phage, sibiromycin decreased the bouyant density of these DNA species to a similiar extent. The antibiotic does not induce single-strand breaks in DNA in vitro as follows from the results of ethidium bromide-CsCl density gradient centrifugation of covalently closed PM-2 DNA.