Mark Pallen m.pallen at ic.ac.uk
Fri Jul 5 11:37:31 EST 1996

jdoliver at MBIO.MBIO.NCSU.EDU ("James D. Oliver") wrote:
>Can anyone tell me anything about the mutability of rpoS (katF)?  Is 
>it a hypermutable gene?  

Interesting question. There seems to be a growing and puzzling 
literature on mutations in rpoS. These papers you may have already seen:
Nucleic Acids Res 20: 5479-80 (1992)[93065224] 

DNA base sequence variability in katF (putative sigma
factor) gene of Escherichia coli.

A. Ivanova, M. Renshaw, R. V. Guntaka & A. Eisenstark
Science 259: 1757-60 (1993)[93206120] 

Microbial competition: Escherichia coli mutants that
take over stationary phase cultures.

M. M. Zambrano, D. A. Siegele, M. Almiron, A. Tormo & R. Kolter

Department of Microbiology and Molecular Genetics, Harvard Medical 
School, Boston, MA

Many microorganisms, including Escherichia coli, can survive extended 
periods of starvation. The
properties of cells that survived prolonged incubation in stationary 
phase were studied by mixture
of 10-day-old (aged) cultures with 1-day-old (young) cultures of the 
same strain of Escherichia
coli. Mutants from the aged cultures that could grow eventually took 
over the population, which
resulted in the death of the cells from the young cultures. This 
phenotype was conferred by
mutations in rpoS, which encodes a putative stationary phase-specific 
sigma factor. These rapid
population shifts have implications for the studies of microbial 
evolution and ecology. 

FEMS Microbiol Lett 126: 171-176 (1995)[95220644] 

The live oral typhoid vaccine Ty21a is a rpoS mutant
and is susceptible to various environmental stresses.

V. Robbe-Saule, C. Coynault & F. Norel

Institut Pasteur, Unite des Enterobacteries, INSERM U389, Paris, France. 

The rpoS (katF) gene, which encodes a RNA polymerase sigma factor (sigma 
s), regulates the
virulence of Salmonella typhimurium in mice. In the present study, we 
show that rpoS mutants can
be frequently found among laboratory strains of Salmonella. In addition, 
a rpoS mutation was
identified in the S. typhi live oral vaccine Ty21a. Introduction of a 
wild-type rpoS gene in Ty21a
allowed the bacteria to survive better under starvation conditions and 
increased their resistance to
other stresses. These results contribute to a better understanding of 
the genetic background of the
live typhoid oral vaccine Ty21a and suggest that the rpoS mutation may 
contribute to the safety of
this strain in humans.

In addition to this, I gather from a brief glimpse at the ASM meeting 
abstracts that the lab strain of salmonella of LT2 is also an rpoS 
mutant and this underlies its low pathogenicity.

So, it looks as if mutants in rpoS are commonly selected for, for 
whatever reason?!

Why are you interested in rpoS?

Dr Mark Pallen, Senior Lecturer in Medical Microbiology,
St Bartholomew's Hospital Medical College, London, EC1A 7BE
currently on a Research Leave Fellowship at Imperial College 
Rm 502, Dept of Biochem, Imperial College, London, SW7 2AY
email:m.pallen at ic.ac.uk  WWW: http://www.qmw.ac.uk/~rhbm001/mpallen.html
phone: day ++44(0)1715945254, eves ++44(0)1815057937, FAX 
Author, Microbial Underground: http://www.qmw.ac.uk/~rhbm001
"Presume not mice to scan, the proper study of mankind is man"
(not) Alexander Pope

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