SOS Regulation of the Type III Secretion System of Enteropathogenic Escherichia coli

Biology Department, Reed College, 3203 S.E. Woodstock Blvd. Portland, OR 97202; Department of Laboratory Medicine, UCSF 0874 SFGH Bldg. 80, Wd. 84, 1001 Potrero Ave. San Francisco, CA 94110

^* To whom correspondence should be addressed. Email: jay.mellies{at}reed.edu.

	Abstract

Genomes of bacterial pathogens encode, and coordinately regulate virulence-associated genes in order to cause disease. Enteropathogenic Escherichia coli (EPEC), a major cause of watery diarrhea in infants and a model Gram-negative pathogen, expresses a type III secretion system (TTSS) that is encoded by the locus of enterocyte effacement (LEE) and is necessary for causing attaching and effacing intestinal lesions. Effector proteins encoded by the LEE and in cryptic prophage are injected into the host cell cytoplasm by the TTS apparatus, ultimately leading to diarrhea. The LEE is comprised of multiple polycistronic operons, most of which are controlled by the global, positive regulator Ler. Here we demonstrated that the LEE2 and LEE3 operons also respond to SOS signaling and this regulation was LexA-dependent. By DNase I protection assay, purified LexA protein bound in vitro to a predicted SOS box located in the divergent, overlapping LEE2/LEE3 promoters. Expression of the lexA1 allele, encoding an uncleavable LexA protein in EPEC, resulted in reduced secretion, particularly in the absence of the Ler regulator. Finally, we present evidence that the cryptic phage-located nleA gene encoding an effector molecule is SOS regulated. Thus we demonstrate, for the first time to our knowledge, that genes encoding components of a TTSS are regulated by the SOS response, and these data might explain how a subset of EPEC effector proteins, encoded within cryptic prophage, are coordinately regulated with the LEE-encoded TTSS necessary for their translocation into host cells.