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J. Bacteriol., Feb 1996, 961-970, Vol 178, No. 4
SL Doty, MC Yu, JI Lundin, JD Heath and EW Nester
The transmembrane sensor protein VirA activates VirG in response to high
levels of acetosyringone (AS). In order to respond to low levels of AS,
VirA requires the periplasmic sugar-binding protein ChvE and
monosaccharides released from plant wound sites. To better understand how
VirA senses these inducers, the C58 virA gene was randomly mutagenized, and
14 mutants defective in vir gene induction and containing mutations which
mapped to the input domain of VirA were isolated. Six mutants had single
missense mutatiions in three widely separated areas of the periplasmic
domain. Eight mutants had mutations in or near an amphipathic helix, TM1,
or TM2. 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. This suggests that most of the periplasmic
domain is required for the interaction with, or response to, ChvE. Three of
the mutations from outside the periplasmic domain, one from each
transmembrane domain and one from the amphiphathic helix, were made in A6
virA. These mutants were defective in the vir gene response to AS. These
mutations did not affect the stability or topology of VirA or prevent
dimerization; therefore, they may interfere with detection of AS or
transmission of the signals to the kinase domain. Characterization of C58
chvE mutants revealed that, unlike A6 VirA, C58 VirA requires ChvE for
activation of the vir genes.
Copyright © 1996, American Society for Microbiology
Mutational analysis of the input domain of the VirA protein of Agrobacterium tumefaciens
Department of Microbiology, University of Washington, Seattle 98195, USA.
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