Disease relevance of virA

• Characterization of the virA virulence gene of the nopaline plasmid, pTiC58, of Agrobacterium tumefaciens [1].
• However, virA and virG are insufficient to activate transcription from virulence gene promoters within Escherichia coli cells, indicating a requirement for additional A. tumefaciens genes [2].

High impact information on virA

• The virA gene of Agrobacterium tumefaciens encodes an inner membrane that mediates the transcriptional activation of virulence genes in response to plant signal molecules [3].
• The pTiAg162 virA locus was shown to be ineffective at directing vir gene induction, suggesting that this may in part contribute to the narrow host range conferred by this plasmid [4].
• We have determined the nucleotide sequence of virA loci from limited (pTiAg162) and wide (pTiA6) host range tumor-inducing (Ti) plasmids, each of which encodes a single protein of 92,000 daltons [4].
• Agrobacterium A136 harboring plasmid pGP159, which contains virA, virG, and a reporter virB:lacZ gene fusion, was mutagenized with UV light or nitrosoguanidine [5].
• Crude protein extracts of induced and uninduced octopine wild-type strain of Agrobacterium tumefaciens, as well as several mutants of the virulence loci virA, -B, -G, -C, -D, and -E, were probed with single- and double-stranded synthetic oligodeoxynucleotides of different sequence and length in an electrophoretic retardation assay [6].

Chemical compound and disease context of virA

• Mutants of the Agrobacterium tumefaciens virA gene exhibiting acetosyringone-independent expression of the vir regulon [7].

Biological context of virA

• A trpE::virA gene fusion was used to confirm the reading frame of virA [1].
• We have determined the complete nucleotide sequence of a 4.8 kilobase fragment encompassing the virA locus of the nopaline-type plasmid, pTiC58, of Agrobacterium tumefaciens. virA is composed of a single open reading frame of 2499 nucleotides, capable of encoding a protein of 91.3 kiloDaltons [1].
• One virA (Ais) mutant, virA112, exhibited vir gene expression in the absence of inducing monosaccharides and acidic growth conditions, both of which are normally required for vir gene induction [7].
• It was found to be a DNA-binding protein that preferentially bound DNA fragments containing the 5' nontranscribed regions of the virA, -B, -C, -D, and -G operons [8].
• However, Ti-plasmids with mutations in virA or virG were unable to confer the responsive phenotype [9].

Associations of virA with chemical compounds

• High nucleotide and amino acid sequence homologies were observed between pTiC58 virA and the virA sequences of three octopine-type plasmids [1].
• The isolation was based on the activation of both virB::lacZ and virE::cat fusions by mutant virA loci in the absence of acetosyringone [7].
• We also evaluated other phenolic compounds in induction assays and observed significant expression with syringealdehyde, a low level of expression with acetovanillone, and no expression with hydroxyacetophenone, similar to what occurs in A. tumefaciens strain A348 from which the virA clone was derived [10].
• Since the trp promoter is not under virA-virG control, this result indicates that modification of VirG is necessary for its full activity [8].
• Four of the mutations in the periplasmic domain, when introduced into the corresponding A6 virA sequence, caused a specific defect in the vir gene response to glucose [11].

Other interactions of virA

• The virA and virG gene products are required for the regulation of the vir regulon on the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens [12].

References