VirB6 is required for stabilization of VirB5 and VirB3 and formation of VirB7 homodimers in Agrobacterium tumefaciens.

Hapfelmeier, Siegfried; Domke, N; Zambryski, P C; Baron, C (2000). VirB6 is required for stabilization of VirB5 and VirB3 and formation of VirB7 homodimers in Agrobacterium tumefaciens. Journal of bacteriology, 182(16), pp. 4505-4511. American Society for Microbiology 10.1128/JB.182.16.4505-4511.2000

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VirB6 from Agrobacterium tumefaciens is an essential component of the type IV secretion machinery for T pilus formation and genetic transformation of plants. Due to its predicted topology as a polytopic inner membrane protein, it was proposed to form the transport pore for cell-to-cell transfer of genetic material and proteinaceous virulence factors. Here, we show that the absence of VirB6 leads to reduced cellular levels of VirB5 and VirB3, which were proposed to assist T pilus formation as minor component(s) or assembly factor(s), respectively. Overexpression of virB6 in trans restored levels of cell-bound and T pilus-associated VirB5 to wild type but did not restore VirB3 levels. Thus, VirB6 has a stabilizing effect on VirB5 accumulation, thereby regulating T pilus assembly. In the absence of VirB6, cell-bound VirB7 monomers and VirB7-VirB9 heterodimers were reduced and VirB7 homodimer formation was abolished. This effect could not be restored by expression of VirB6 in trans. Expression of TraD, a component of the transfer machinery of the IncN plasmid pKM101, with significant sequence similarity to VirB6, restored neither protein levels nor bacterial virulence but partly permitted T pilus formation in a virB6 deletion strain. VirB6 may therefore regulate T pilus formation by direct interaction with VirB5, and wild-type levels of VirB3 and VirB7 homodimers are not required.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Service Sector > Institute for Infectious Diseases > Research

UniBE Contributor:

Hapfelmeier, Siegfried Hektor




American Society for Microbiology




Siegfried Hektor Hapfelmeier-Balmer

Date Deposited:

04 May 2015 12:36

Last Modified:

26 Jun 2016 02:01

Publisher DOI:


PubMed ID:


Additional Information:

Notes: PMC94622 Custom 1: papers3://publication/uuid/49B0D520-F85C-4CE1-9917-6F3DADF12683 Date: 2000


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