Disease relevance of virB1

• In a search for these additional genes, we have identified the rpoA gene, encoding the alpha subunit of RNA polymerase (RNAP), which confers significant expression of a virB promoter (virBp)::lacZ fusion in E. coli in the presence of an active transcriptional regulator virG gene [1].
• We here report a heterologous complementation in the case of A. tumefaciens virB1 defects with its orthologs from Brucella suis (VirB1s) and the IncN plasmid pKM101 (TraL) [2].
• Transferred DNA (T-DNA)-associated proteins of Agrobacterium tumefaciens are exported independently of virB [3].
• The gene encoding the 17-kDa antigen of Bartonella henselae is located within a cluster of genes homologous to the virB virulence operon [4].
• The virB operon has been associated with the transfer of oncogenic T-DNA in Agrobacterium tumefaciens and with secretion of the pertussis toxin in Bordetella pertussis [4].

High impact information on virB1

• The two largest vir operons, virB and virD, are probably polycistronic [5].
• Our data suggest that VirD2, VirE2, and VirF are transported across the cytoplasmic membrane by a specific pathway, independent of virB [3].
• The Ti plasmid increases the efficiency of Agrobacterium tumefaciens as a recipient in virB-mediated conjugal transfer of an IncQ plasmid [6].
• A. tumefaciens C58C1 containing Ti-plasmids with Tn5 insertions in virB, C, D or E exhibited marked chemotaxis towards acetosyringone [7].
• A virGN54D mutant gene of M. loti caused constitutive expression of lacZ reporter gene fusions to virB1, virD4, msi059, and msi061 [8].

Biological context of virB1

• Gene reporter studies demonstrated that the B. abortus virB locus constitutes an operon transcribed from virB1 which is turned on during the stationary phase of growth [9].
• The B. abortus virB locus is a collinear arrangement of 13 open reading frames (ORFs) [9].
• Previous genetic analysis of the approximately 9.5-kilobase-pair virB operon has been limited to transposon insertion mutagenesis [10].
• 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 [11].
• Recent comparative amino acid sequence studies of the products of these vir genes have revealed interesting similarities between Tra proteins of Escherichia coli F factor, which are involved in the biosynthesis and assembly of a conjugative pilus, and VirB proteins encoded by genes of the virB operon of A. tumefaciens pTiC58 [12].

Anatomical context of virB1

• A B. abortus polar virB1 mutant failed to replicate in HeLa cells, indicating that the virB operon plays a critical role in intracellular multiplication [9].
• Promiscuous DNA transfer system of Agrobacterium tumefaciens: role of the virB operon in sex pilus assembly and synthesis [13].
• The virB operon of A. tumefaciens encodes 11 proteins, of which 9 are known to be located in the membranes and 10 have been shown to be essential for virulence [14].
• The virB gene products of the Agrobacterium tumefaciens tumor-inducing (Ti) plasmid have been proposed to mediate T-DNA transport through the bacterial cell wall into plant cells [10].

Analytical, diagnostic and therapeutic context of virB1

• Sequence analysis of the recombinant clone, pBHIM-2, revealed that the open reading frame (ORF) encoding the 17-kDa antigen was situated between homologs of virB4 and virB6, two genes that belong to the virB operon [4].

References