Genetic analysis of a bacterial genetic exchange element: The gene transfer agent of Rhodobacter capsulatus
- Department of Microbiology and Immunology, University of British Columbia, 6174 University Boulevard, Vancouver, British Columbia, Canada, V6T 1Z3
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Edited by Robert Haselkorn, The University of Chicago, Woods Hole, MA, and approved November 1, 1999 (received for review September 1, 1999)
Abstract
An unusual system of genetic exchange exists in the purple nonsulfur bacterium Rhodobacter capsulatus. DNA transmission is mediated by a small bacteriophage-like particle called the gene transfer agent (GTA) that transfers random 4.5-kb segments of the producing cell's genome to recipient cells, where allelic replacement occurs. This paper presents the results of gene cloning, analysis, and mutagenesis experiments that show that GTA resembles a defective prophage related to bacteriophages from diverse genera of bacteria, which has been adopted by R. capsulatus for genetic exchange. A pair of cellular proteins, CckA and CtrA, appear to constitute part of a sensor kinase/response regulator signaling pathway that is required for expression of GTA structural genes. This signaling pathway controls growth-phase-dependent regulation of GTA gene messages, yielding maximal gene expression in the stationary phase. We suggest that GTA is an ancient prophage remnant that has evolved in concert with the bacterial genome, resulting in a genetic exchange process controlled by the bacterial cell.
Footnotes
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↵ * To whom correspondence and reprint requests should be addressed. E-mail: jbeatty{at}interchange.ubc.ca.
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This paper was submitted directly (Track II) to the PNAS office.
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Data deposition: The DNA sequences reported in this paper have been deposited in the GenBank database [accession nos. AF181078 (ctrA), AF181079 (cckA), and AF181080 (part of GTA gene cluster)].
- Abbreviation:
- GTA,
- gene-transfer agent
- Copyright © 2000, The National Academy of Sciences
