JB
Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Lai, E.-M.
Right arrow Articles by Kado, C. I.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Lai, E.-M.
Right arrow Articles by Kado, C. I.

J Bacteriol, May 1998, p. 2711-2717, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Processed VirB2 Is the Major Subunit of the Promiscuous Pilus of Agrobacterium tumefaciens

Erh-Min Lai and Clarence I. Kado*

Davis Crown Gall Group, University of California, Davis, California 95616

Received 23 December 1997/Accepted 10 March 1998

Previous studies have implicated the obligatory requirement for the vir regulon (or "virulon") of the Ti plasmid for the transfer of oncogenes from Agrobacterium tumefaciens to plant cells. The machinery used in this horizontal gene transfer has been long thought to be a transformation or conjugative delivery system. Based on recent protein sequence comparisons, the proteins encoded by the virB operon are strikingly similar to proteins involved in the synthesis and assembly of conjugative pili such as the conjugative pilus of F plasmid in Escherichia coli. The F pilus is composed of TraA pilin subunits derived from TraA propilin. In the present study, evidence is provided showing that the counterpart of TraA is VirB2, which like TraA propilin is processed into a 7.2-kDa product that comprises the pilus subunit as demonstrated by biochemical and electron microscopic analyses. The processed VirB2 protein is present exocellularly on medium on which induced A. tumefaciens had grown and appears as thin filaments of 10 nm that react specifically to VirB2 antibody. Exocellular VirB2 is produced abundantly at 19°C as compared with 28°C, an observation that parallels the effect of low temperature on the production of vir gene-specific pili observed previously (K. J. Fullner, L. C. Lara, and E. W. Nester, Science 273:1107-1109, 1996). Export of the processed VirB2 requires other virB genes since mutations in these genes cause the loss of VirB2 pilus formation and result in processed VirB2 accumulation in the cell. The presence of exocellular processed VirB2 is directly correlated with the formation of pili, and it appears as the major protein in the purified pilus preparation. The evidence provides a compelling argument for VirB2 as the propilin whose 7.2-kDa processed product is the pilin subunit of the promiscuous conjugative pilus, hereafter called the "T pilus" of A. tumefaciens.

* Corresponding author. Mailing address: Davis Crown Gall Group, University of California, One Shields Ave., Davis, CA 95616. Phone: (530) 752-0325. Fax: (530) 752-5674. E-mail: cikado{at}ucdavis.edu.

J Bacteriol, May 1998, p. 2711-2717, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


This article has been cited by other articles:



Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
Appl. Environ. Microbiol. Infect. Immun. Eukaryot. Cell
Mol. Cell. Biol. J. Virol. Microbiol. Mol. Biol. Rev.
ALL ASM JOURNALS

Copyright © 1998 by the American Society for Microbiology. All rights reserved.