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Infection and Immunity, December 2001, p. 7858-7865, Vol. 69, No. 12
Department of Microbiology, Dartmouth Medical
School, Hanover, New Hampshire 03755,1 and
Department of Immunology, Microbiology, Pathology, and
Infectious Diseases, Karolinska Institutet, Huddinge University
Hospital, S-141 86 Huddinge, Sweden2
Received 12 July 2001/Returned for modification 13 August
2001/Accepted 5 September 2001
Two genes of the sigB operon,
rsbU and rsbV, were deleted in an
rsbU+ strain (FDA486) to evaluate the
contribution of these two genes to
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.12.7858-7865.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
B Activity in Staphylococcus
aureus Is Controlled by RsbU and an Additional Factor(s) during
Bacterial Growth
B activity in
Staphylococcus aureus. The
B protein
level and the transcription of two
B-dependent promoters
(sigB and sarA P3 transcripts)
were analyzed in the constructed mutants. A deletion of the first gene
(rsbU) within the sigB operon led only to
a partial reduction in 
activity. A deletion of the
second gene (rsbV) resulted in a more dramatic reduction
in the
B protein level and its activity than did the
deletion of rsbU, thus indicating that RsbV can be
activated independent of RsbU. In the parental strain, the
B-dependent transcript initiated upstream of
rsbV was 28-fold higher than the
A-dependent transcript originating from the
rsbU promoter. The level of the
B-dependent transcript decreased up to 50% in the
rsbU mutant and up to 90% in the rsbV
mutant compared with the transcript in the wild type. The yellow
pigment of S. aureus colonies, a
B-dependent phenotype, was partially reduced in the
rsbU and rsbV mutants, whereas
alpha-hemolysin was increased. Additionally, the sarA P3
promoter activity of the parental strain was induced to a higher level
in response to pH 5.5 than was that of the rsbU or
rsbV mutant, indicating that RsbU is the major activator
of the
B response to acid stress. Using a
tetracycline-inducible system to modulate the expression of RsbW, we
progressively repressed pigment production, presumably by reducing the
free
B level. Collectively, our data indicated that RsbU
and RsbV in S. aureus contributed to
different levels of
B protein expression and varying
B activities. Although RsbV can activate
B independent of RsbU, RsbU remains the major activator
of
B during acid stress.
*
Corresponding author. Mailing address: Department of
Microbiology, Dartmouth Medical School, Vail 206, Hanover, NH 03755. Phone: (603) 650-1310. Fax: (603) 650-1362. E-mail:
Ambrose.Cheung{at}Dartmouth.EDU.
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