Journal of Bacteriology, October 1999, p. 6361-6370, Vol. 181, No. 20
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Molecular
Genetics1 and Genetic Strains Research
Center,
Received 7 June 1999/Accepted 13 August 1999
The genome DNA of Escherichia coli is associated with
about 10 DNA-binding structural proteins, altogether forming the
nucleoid. The nucleoid proteins play some functional roles, besides
their structural roles, in the global regulation of such essential DNA functions as replication, recombination, and transcription. Using a
quantitative Western blot method, we have performed for the first time
a systematic determination of the intracellular concentrations of
12 species of the nucleoid protein in E. coli W3110,
including CbpA (curved DNA-binding protein A), CbpB (curved
DNA-binding protein B, also known as Rob [right origin binding
protein]), DnaA (DNA-binding protein A), Dps (DNA-binding protein from
starved cells), Fis (factor for inversion stimulation), Hfq (host
factor for phage Q
), H-NS (histone-like nucleoid
structuring protein), HU (heat-unstable nucleoid protein), IciA
(inhibitor of chromosome initiation A), IHF (integration host factor),
Lrp (leucine-responsive regulatory protein), and StpA (suppressor of
td mutant phenotype A). Intracellular protein levels reach
a maximum at the growing phase for nine proteins, CbpB (Rob), DnaA,
Fis, Hfq, H-NS, HU, IciA, Lrp, and StpA, which may play regulatory
roles in DNA replication and/or transcription of the growth-related
genes. In descending order, the level of accumulation, calculated in
monomers, in growing E. coli cells is Fis, Hfq, HU, StpA,
H-NS, IHF*, CbpB (Rob), Dps*, Lrp, DnaA, IciA, and CbpA* (stars
represent the stationary-phase proteins). The order of abundance, in
descending order, in the early stationary phase is Dps*, IHF*, HU, Hfq,
H-NS, StpA, CbpB (Rob), DnaA, Lrp, IciA, CbpA, and Fis, while that in
the late stationary phase is Dps*, IHF*, Hfq, HU, CbpA*, StpA, H-NS,
CbpB (Rob), DnaA, Lrp, IciA, and Fis. Thus, the major protein
components of the nucleoid change from Fis and HU in the growing phase
to Dps in the stationary phase. The curved DNA-binding protein, CbpA, appears only in the late stationary phase. These changes in the composition of nucleoid-associated proteins in the stationary phase are
accompanied by compaction of the genome DNA and silencing of the genome functions.
*
Corresponding author. Mailing address: Department of
Molecular Genetics, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan. Phone: 81-559-81-6741. Fax: 81-559-81-6746. E-mail: aishiham{at}lab.nig.ac.jp.
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