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Journal of Bacteriology, April 1999, p. 2124-2131, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Stabilization of the Relaxosome and Stimulation of Conjugal Transfer Are Genetically Distinct Functions of the R1162 Protein MobB

Tariq Perwez and Richard J. Meyer*

Department of Microbiology and Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712

Received 28 October 1998/Accepted 19 January 1999

MobB is a small protein encoded by the broad-host-range plasmid R1162 and required for efficient mobilization of its DNA during conjugation. The protein was shown previously to stabilize the relaxosome, the complex of plasmid DNA and mobilization proteins at the origin of transfer (oriT). We have generated in-frame mobB deletions that specifically inactivate the stabilizing effect of MobB while still allowing a high rate of transfer. Thus, MobB has two genetically distinct functions in transfer. The effect of another deletion, extending into mobA, indicates that both functions require a specific region of MobA protein that is distinct from the nicking-ligating domain. The mobB mutations that specifically affected stability also resulted in poor growth of cells, due to increased transcription from the promoters adjacent to oriT. The effects of the mutations could be suppressed not only by full-length MobB provided in trans, as expected, but also by additional copies of oriT, cloned in pBR322. In addition, in the presence of MobA both the full-length and truncated forms of MobB stimulated recombination between oriT-containing plasmids. We propose a model in which MobB regulates expression of plasmid genes by altering the stability of the relaxosome, in a manner that involves the coupling of plasmid molecules.

* Corresponding author. Mailing address: Department of Microbiology and Institute for Cellular and Molecular Biology, University of Texas, Austin, TX 78712. Phone: (512) 471-3817. Fax: (512) 471-7088. E-mail: rmeyer{at}mail.utexas.edu.

Journal of Bacteriology, April 1999, p. 2124-2131, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


This article has been cited by other articles:

  • Jandle, S., Meyer, R. (2006). Stringent and Relaxed Recognition of oriT by Related Systems for Plasmid Mobilization: Implications for Horizontal Gene Transfer. J. Bacteriol. 188: 499-506 [Abstract] [Full Text]  
  • Zhang, X., Zhang, S., Meyer, R. J. (2003). Molecular handcuffing of the relaxosome at the origin of conjugative transfer of the plasmid R1162. Nucleic Acids Res 31: 4762-4768 [Abstract] [Full Text]  
  • Meyer, R. (2000). Identification of the mob Genes of Plasmid pSC101 and Characterization of a Hybrid pSC101-R1162 System for Conjugal Mobilization. J. Bacteriol. 182: 4875-4881 [Abstract] [Full Text]  
  • Henderson, D., Meyer, R. (1999). The MobA-Linked Primase Is the Only Replication Protein of R1162 Required for Conjugal Mobilization. J. Bacteriol. 181: 2973-2978 [Abstract] [Full Text]  


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