title: Toroidal nucleoids in Escherichia coli exposed to chloramphenicol.
abstract: The DNA of growing cells of Escherichia coli occurs in one or a few lobular bodies known as nucleoids. Upon exposure to chloramphenicol, the nucleoids assume compact, rounded forms ("cm-nucleoids") that have been described as ring- or sphere-shaped. Multiple views of single cells or spheroplasts, however, support a different, curved toroid shape for cm-nucleoids. The multiple views were obtained either by DNA fluorescence imaging as the cells or spheroplasts reoriented in liquid medium or by optical sectioning using phase-contrast or fluorescence imaging of immobilized cells. The curved toroid shape is consistent with electron microscope images of thin sections of chloramphenicol-treated cells. The relationship of this structure to active and inactive nucleoids and to the smaller toroidal forms made by in vitro DNA condensation is discussed.
authors.affiliation: Laboratory of Molecular Biology, National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Building 5, Room 329, Bethesda, MD 20892-0560, USA. stevenz@bdg5.niddk.nih.gov
authors.forename: Steven B
authors.initials: SB
authors.lastname: Zimmerman
mesh_terms: D002455:Cell Division; D002701:Chloramphenicol / Q000494:pharmacology*; D004247:DNA / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008856:Microscopy, Fluorescence; D009690:Nucleic Acid Conformation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012685:Sepharose / Q000494:pharmacology
chemical_list: D011500:Protein Synthesis Inhibitors; D002701:Chloramphenicol; D004247:DNA; D012685:Sepharose