Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: February 22, 2002
Publication Date: N/A
Technical Abstract: Production of Shiga toxins and attaching and effacing lesions (A/E lesions) are important virulence attributes of enterohemorrhagic Escherichia coli (EHEC) O157:H7. The genetic information essential for the formation of A/E lesions is contained in a locus of enterocyte effacement (LEE). LEE encodes for a type III secretion system, intimin, Tir and secreted proteins EspA, EspD, and EspB. The genes espA, espD, and espB, encoding Esp proteins, are organized into a single operon. The Esp proteins are required for signal transduction events leading to the formation of A/E lesions. However, neither the mechanism of transcriptional regulation of Esp proteins nor the signals activating the expression of these genes are fully understood. In order to identify genes regulating transcription of the esp operon, an EHEC O157:H7 strain containing a transcriptional fusion between the esp operon and a promoterless lac reporter was constructed. Determination of b-galactosidase activity of this fusion (esp::lac) showed a very low level of growth-dependent expression of b- galactosidase. Transposon mutagenesis of the esp::lac strain facilitated identification of clones expressing 10-fold higher b- galactosidase activity. Nucleotide sequence analysis of DNA flanking the transposon insertion site resulted in identification of an ORF that we have named as Esp-regulator. Reintroduction of Esp-regulator into the esp::lac strain carrying a transposon insertion restored low levels of b-galactosidase activity observed in the parent esp::lac strain. These results indicate that Esp-regulator is a negative modulator of the expression of Esp proteins.