Affiliation:
1. Center for Vaccine Development, Departments of Pediatrics, Medicine, and Microbiology & Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201
Abstract
ABSTRACT
Most strains of
Shigella flexneri
2a and enteroaggregative
Escherichia coli
carry a highly conserved chromosomal locus which encodes a 109-kDa secreted mucinase (called Pic) and, on the opposite strand in overlapping fashion, an oligomeric enterotoxin called ShET1, encoded by the
setA
and
setB
genes. Here, we characterize the genetic regulation of these overlapping genes. Our data suggest that
pic
and the
setBA
loci are transcribed as complementary 4-kb mRNA species. The major
pic
promoter is maximally activated at 37°C in exponential growth phase. Our data suggest that the
setB
gene is transcribed from a promoter which lies more than 1.5 kb upstream of the
setB
structural gene;
setA
may be transcribed via readthrough of the
setB
transcript and possibly by its own promoter. The long leader of the
setB
gene provides a strong silencing effect on
setB
transcription. The signals which provide relief from
setB
silencing are not clear, but significant induction is observed in a continuous anaerobic culture of human fecal bacteria, suggesting that some complex characteristics of the human intestine act to lift repression of
setB
expression. Our studies provide the first insights into the mechanisms affecting expression of this unusual virulence locus.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
46 articles.
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