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Proc Natl Acad Sci U S A. 1991 Sep 15;88(18):8184-8.

Membrane-bounded nucleoid in the eubacterium Gemmata obscuriglobus.

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Department of Microbiology, University of Queensland, Brisbane, Queensland, Australia.


The freshwater budding eubacterium Gemmata obscuriglobus possesses a DNA-containing nuclear region that is bounded by two nuclear membranes. The membrane-bounded nature of the nucleoid in this bacterium was shown by thin sectioning of chemically fixed cells, thin sectioning of freeze-substituted cells, and freeze-fracture/freeze-etch. The fibrillar nucleoid was surrounded by electron-dense granules that were in turn enveloped by two nuclear membranes separated by an electron-transparent space. Immunogold labeling of thin sections of conventionally fixed cells with anti-double-stranded DNA antibody demonstrated double-stranded DNA associated with fibrillar material within the membrane boundary. The occurrence of a membrane-bounded nucleoid in a eubacterial prokaryote is a significant exception to the evidence supporting the prokaryote/eukaryote dichotomous classification of cell structure.

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