title: Transcription of the ehx enterohemolysin gene is positively regulated by GrlA, a global regulator encoded within the locus of enterocyte effacement in enterohemorrhagic Escherichia coli.
abstract: The pathogenicity island termed locus of enterocyte effacement (LEE) encodes a type 3 protein secretion system, whose function is required for full virulence of enterohemorrhagic Escherichia coli (EHEC). GrlR and GrlA are LEE-encoded negative and positive regulators, respectively, for controlling transcription of the ler gene, which encodes a central activator of LEE gene expression. We previously reported that the GrlR-GrlA regulatory system controls not only the LEE genes but also flagellar gene expression in EHEC (S. Iyoda et al., J. Bacteriol. 188:5682-5692, 2006). In order to further explore virulence-related genes under the control of the GrlR-GrlA regulatory system, we characterized a grlR-deleted EHEC O157 strain, which was found to have high and low levels of expression of LEE and flagellar genes, respectively. We report here that the grlR deletion significantly induced enterohemolysin (Ehx) activity of EHEC O157 on plates containing defibrinated sheep erythrocytes. Ehx levels were not induced in the grlR grlA double mutant strain but increased markedly by overexpression of GrlA even in the ler mutant, indicating that GrlA is responsible for this regulation. Ehx of the EHEC O157 Sakai strain is encoded by the ehxCABD genes, which are carried on the large plasmid pO157. The expression of ehxC fused with FLAG tag or a promoterless lacZ gene on pO157 was significantly induced under conditions in which GrlA was overproduced. These results together suggest that GrlA acts as a positive regulator for the ehx transcription in EHEC.
authors.affiliation: Department of Bacteriology, Infectious Disease Surveillance Center, National Institute of Infectious Diseases, Tokyo 162-8640, Japan.
authors.forename: Takehito
authors.initials: T
authors.lastname: Saitoh
authors.forename: Sunao
authors.initials: S
authors.lastname: Iyoda
authors.forename: Shouji
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Yan
authors.initials: Y
authors.lastname: Lu
authors.forename: Ken
authors.initials: K
authors.lastname: Shimuta
authors.forename: Makoto
authors.initials: M
authors.lastname: Ohnishi
authors.forename: Jun
authors.initials: J
authors.lastname: Terajima
authors.forename: Haruo
authors.initials: H
authors.lastname: Watanabe
mesh_terms: D019677:Artificial Gene Fusion; D001427:Bacterial Toxins / Q000096:biosynthesis*; D003470:Culture Media / Q000737:chemistry; D019453:Escherichia coli O157 / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D005407:Flagella / Q000235:genetics; D017353:Gene Deletion; D018628:Gene Dosage; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D006461:Hemolysis; D010750:Phosphoproteins; D010957:Plasmids; D012097:Repressor Proteins / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015854:Up-Regulation; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D001427:Bacterial Toxins; D003470:Culture Media; C097321:EHEC-hlyA protein, E coli; D029968:Escherichia coli Proteins; C513430:GrlA protein, E coli; C513429:GrlR protein, E coli; C457340:LEE protein, E coli; D010750:Phosphoproteins; D012097:Repressor Proteins; D015534:Trans-Activators; D001616:beta-Galactosidase