title: The ZorO-OrzO type I toxin-antitoxin locus: repression by the OrzO antitoxin.
abstract: Type I toxin-antitoxin loci consist of two genes: a small, hydrophobic, potentially toxic protein, and a small RNA (sRNA) antitoxin. The sRNA represses toxin gene expression by base pairing to the toxin mRNA. A previous bioinformatics search predicted a duplicated type I locus within Escherichia coli O157:H7 (EHEC), which we have named the gene pairs zorO-orzO and zorP-orzP. We show that overproduction of the zorO gene is toxic to E. coli; co-expression of the sRNA OrzO can neutralize this toxicity, confirming that the zorO-orzO pair is a true type I toxin-antitoxin locus. However, OrzO is unable to repress zorO in a strain deleted for RNase III, indicating that repression requires cleavage of the target mRNA. Sequence analysis and mutagenesis studies have elucidated a nucleotide sequence region (V1) that allows differential recognition of the zorO mRNA by OrzO and not OrzP, and a specific single nucleotide within the V1 of OrzO that is critical for repression of zorO. Although there are 18 nt of complementarity between the OrzO sRNA and the zorO mRNA, not all base pairing interactions are needed for repression; however, the amount needed is dependent on whether there is continuous or discontinuous complementarity to the target mRNA.
authors.affiliation: Department of Microbiology, University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Wen
authors.forename: Daniel
authors.initials: D
authors.lastname: Won
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Fozo
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics* / Q000378:metabolism; D020029:Base Pairing; D001483:Base Sequence; D019453:Escherichia coli O157 / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D056426:Genetic Loci; D035001:Host Factor 1 Protein / Q000235:genetics; D008969:Molecular Sequence Data; D058727:RNA, Small Untranslated / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D043244:Ribonuclease III / Q000235:genetics
chemical_list: D001427:Bacterial Toxins; D029968:Escherichia coli Proteins; C087373:Hfq protein, E coli; D035001:Host Factor 1 Protein; D058727:RNA, Small Untranslated; C587788:ZorO protein, E coli; D043244:Ribonuclease III