title: Chromosomal structure of the halophilic archaebacterium Halobacterium salinarium.
abstract: The chromosomal structure of the extremely halophilic archaebacterium Halobacterium salinarium was examined. Sheared chromosomes prepared from the bacteria in the late exponential phase were separated into two peaks (peaks I and II) by sucrose gradient centrifugation, suggesting that the chromosomes consist of two parts differing in quality. The UV spectra of peaks I and II resembled those of DNA and eukaryotic chromatin, respectively. Electron microscopic observations revealed that the major component of peak I was protein-free DNA, while the major components of peak II were rugged thick fibers with a diameter of 17 to 20 nm. The rugged fibers basically consisted of bacterial nucleosome-like structures composed of DNA and protein, as demonstrated in experiments with proteinase and nuclease digestion. Whole-mount electron microscopic observations of the chromosomes directly spread onto a water surface revealed a configuration in which the above-described regions were localized on a continuous DNA fiber. From these results it is concluded that the H. salinarium chromosome is composed of regions of protein-free DNA and DNA associated with nucleosome-like structures. Peaks I and II were predominant in the early exponential phase and stationary phase, respectively; therefore, the transition of the chromosome structure between non-protein-associated and protein-associated forms seems to be related to the bacterial growth phase.
authors.affiliation: Department of Biology, Toho University School of Medicine, Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Takayanagi
authors.forename: S
authors.initials: S
authors.lastname: Morimura
authors.forename: H
authors.initials: H
authors.lastname: Kusaoke
authors.forename: Y
authors.initials: Y
authors.lastname: Yokoyama
authors.forename: K
authors.initials: K
authors.lastname: Kano
authors.forename: M
authors.initials: M
authors.lastname: Shioda
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient / Q000379:methods; D002843:Chromatin / Q000737:chemistry / Q000648:ultrastructure; D002876:Chromosomes, Bacterial / Q000648:ultrastructure*; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification / Q000648:ultrastructure; D006217:Halobacterium / Q000235:genetics* / Q000254:growth & development / Q000648:ultrastructure*; D007700:Kinetics; D008836:Micrococcal Nuclease / Q000378:metabolism; D008854:Microscopy, Electron; D051381:Rats; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002843:Chromatin; D004269:DNA, Bacterial; D008836:Micrococcal Nuclease