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Characterization of the supervirulent virG gene of the Agrobacterium tumefaciens plasmid pTiBo542.
Authors:Chin-Yi Chen  Lu Wang and Stephen C Winans
Institution:(1) Section of Microbiology, Cornell University, 14853 Ithaca, NY, USA
Abstract:Summary The virG gene of the Agrobacterium tumefaciens Ti plasmid pTiBo542 has previously been reported to elicit stronger vir gene expression than its counterpart in the pTiA6 plasmid, a property we call the ldquosuperactivatorrdquo phenotype. The DNA sequence of the pTiBo542 virG gene was determined and compared to that of the pTiA6 gene. The DNA sequences of these genes differ at 16 positions: two differences are in the promoter regions, 12 are in the coding regions, and two are in the 3prime untranslated regions. The 3prime end of the pTiA6 virG gene also contains a probable insertion sequence that is not found downstream of the pTiBo542 gene. The base pair differences in the two coding regions result in only two amino acid differences, both in the amino-terminal halves of the proteins. Five hybrid virG genes were constructed and used to activate the expression of a virB::lacZ gene fusion. Differences in the coding regions of these genes accounted for most of the superactivator phenotype, while differences at the promoter and 3prime untranslated regions also contributed. These findings suggest that the properties of these VirG proteins and their quantities are important for vir gene induction, and also suggest a long-term selective pressure for mutations contributing to differences between these two genes.
Keywords:VirG  Agrobacterium  vir activation  Supervirulence  pTiBo542
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