ORIGINAL PAPER

Molecular and General Genetics MGG

, Volume 257, Issue 4, pp 392-403

First online:

Autoregulation of the partition genes of the mini-F plasmid and the intracellular localization of their products in Escherichia coli

  • M. HiranoAffiliated withDepartment of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan Fax: +81–96–371–2408
  • , H. MoriAffiliated withDepartment of Bioinformatics, Research and Education Center for Genetic Information, Nara Institute of Science and Technology, Takayama-cho 8916-5, Ikoma 630-1, Japan
  • , T. OnogiAffiliated withDepartment of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan Fax: +81–96–371–2408
  • , M. YamazoeAffiliated withDepartment of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan Fax: +81–96–371–2408
  • , H. NikiAffiliated withDepartment of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan Fax: +81–96–371–2408
  • , T. OguraAffiliated withDepartment of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan Fax: +81–96–371–2408
  • , S. HiragaAffiliated withDepartment of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan Fax: +81–96–371–2408

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Abstract

The sopAB operon and the sopC sequence, which acts as a centromere, are essential for stable maintenance of the mini-F plasmid. Immunoprecipitation experiments with purified SopA and SopB proteins have demonstrated that these proteins interact in vitro. Expression studies using the lacZ gene as a reporter revealed that the sopAB operon is repressed by the cooperative action of SopA and SopB. Using immunofluorescence microscopy, we found discrete fluorescent foci of SopA and SopB in cells that produce both SopA and SopB in the presence of the sopC DNA segment, but not in the absence of sopC, suggesting the SopA-SopB complex binds to sopC segments. SopA was exclusively found to colocalize with nucleoids in cells that produced only SopA, while, in the absence of SopA, SopB was distributed in the cytosolic spaces.

Key words F plasmid Plasmid partitioning Autoregulation Immunoprecipitation Immunofluorescence microscopy