title: Multiple molecular species of circular R-factor DNA isolated from Escherichia coli.
mesh_terms: D002876:Chromosomes, Bacterial / Q000032:analysis; D004269:DNA, Bacterial / Q000302:isolation & purification*; D004352:Drug Resistance, Microbial; D004926:Escherichia coli; D008722:Methods; D008854:Microscopy, Electron; D008956:Models, Chemical; D009691:Nucleic Acid Denaturation; D014461:Ultracentrifugation
chemical_list: D004269:DNA, Bacterial