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J. Bacteriol., 06 1996, 3462-3469, Vol 178, No. 12
K Wengelnik and U Bonas
hrp genes, basic pathogenicity genes of the pepper and tomato pathogen
Xanthomonas campestris pv. vesicatoria, are regulated dependent on
environmental conditions. We isolated the hrpXv gene, which was found to be
outside the large hrp cluster comprising the six loci hrpA to hrpF. The
predicted HrpXv protein is 476 amino acids long and has a molecular mass of
52.5 kDa. HrpX is highly conserved among xanthomonads and is a member of
the AraC family of regulatory proteins. An hrpXv insertion mutant has a
typical hrp phenotype and no longer allows induction of the five hrp loci
hrpB to hrpF in the new hrp induction medium XVM2, indicating that HrpXv is
the positive regulator of these loci. An hrpXv mutant could be partially
complemented by the related hrpB gene of Burkholderia solanacearum, the
protein product of which shows 40 and 58% amino acid identity and
similarity, respectively, to HrpXv. The hrpXv gene itself has a low basal
level of expression that is enhanced in XVM2. Expression of hrpXv as well
as that of the hrpA locus is independent of the hrpXv gene. The
transcription start site of hrpXv was mapped. Comparison between the hrpXv
promoter and the corresponding region of the hrpXc gene from X. campestris
pv. campestris revealed sequence conservation up to position -84. A
putative helix-turn-helix motif in the C-terminal region of HrpXv and its
possible interaction with a conserved hrp promoter element, the
plant-inducible promoter box, are discussed.
Copyright © 1996, American Society for Microbiology
HrpXv, an AraC-type regulator, activates expression of five of the six loci in the hrp cluster of Xanthomonas campestris pv. vesicatoria
Institut des Sciences Vegetales, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
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