Journal of Bacteriology, June 1999, p. 3409-3418, Vol. 181, No. 11
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Microbial Pathogenicity and Vaccine Research, Division of Microbiology, GBF-National Research Centre for Biotechnology, D-38124 Braunschweig, Germany
Received 21 December 1998/Accepted 31 March 1999
We have determined that the genes encoding the secreted proteins
EspA, EspD, and EspB of enterohemorrhagic Escherichia coli (EHEC) are organized in a single operon. The esp operon is
controlled by a promoter located 94 bp upstream from the ATG start
codon of the espA gene. The promoter is activated in the
early logarithmic growth phase, upon bacterial contact with eukaryotic
cells and in response to Ca2+, Mn2+, and HEPES.
Transcription of the esp operon seems to be switched off in
tightly attached bacteria. The activation process is regulated by
osmolarity (induction at high osmolarities), modulated by temperature, and influenced by the degree of DNA supercoiling. Transcription is
S dependent, and the H-NS protein contributes to its
fine tuning. Identification of the factors involved in activation of
the esp operon and the signals responsible for modulation
may facilitate understanding of the underlying molecular events leading
to sequential expression of virulence factors during natural infections
caused by EHEC.
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