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Infection and Immunity, June 2000, p. 3758-3762, Vol. 68, No. 6
Department of Microbiology, University of
Texas Health Science Center at San Antonio, San Antonio, Texas
78229-3900,1 and Departments of Medicine
and Microbiology, University of Washington, Seattle, Washington
981952
Received 13 December 1999/Returned for modification 17 February
2000/Accepted 22 March 2000
The PhoP-PhoQ two-component system is necessary for the virulence
of Salmonella spp. and is responsible for regulating
several modifications of the lipopolysaccharide (LPS). Mutagenesis of the transcriptional regulator phoP resulted in the
identification of a mutant able to activate transcription of regulated
genes ~100-fold in the absence of PhoQ. Sequence analysis showed
two single-base alterations resulting in amino acid changes at
positions 93 (S93N) and 203 (Q203R). These mutations were individually
created, and although each resulted in a constitutive phenotype,
the double mutant displayed a synergistic effect both in the induction
of PhoP-activated gene expression and in resistance to
antimicrobial peptides. The constitutive phoP gene was
placed under the control of an arabinose-inducible promoter to examine
the kinetics of PhoP-activated gene induction and the resultant
modifications of LPS. Gene induction and 2-hydroxymyristate
modification of the lipid A were shown to occur within minutes of the
addition of arabinose and to peak at 4 h. As the first
constitutive mutant of phoP identified, this allele will be
invaluable to future genetic and biochemical studies of this and likely
other regulatory systems.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Constitutive Mutations of the Salmonella enterica
Serovar Typhimurium Transcriptional Virulence Regulator
phoP
*
Corresponding author. Mailing address: Department of
Microbiology, Mail code 7758, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229-3900. Phone:
(210) 567-3973. Fax: (210) 567-3795. E-mail:
gunnj{at}uthscsa.edu.
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