title: An SOS-regulated type 2 toxin-antitoxin system.
abstract: The Escherichia coli chromosome encodes seven demonstrated type 2 toxin-antitoxin (TA) systems: cassettes of two or three cotranscribed genes, one encoding a stable toxin protein that can cause cell stasis or death, another encoding a labile antitoxin protein, and sometimes a third regulatory protein. We demonstrate that the yafNO genes constitute an additional chromosomal type 2 TA system that is upregulated during the SOS DNA damage response. The yafNOP genes are part of the dinB operon, of which dinB underlies stress-induced mutagenesis mechanisms. yafN was identified as a putative antitoxin by homology to known antitoxins, implicating yafO (and/or yafP) as a putative toxin. Using phage-mediated cotransduction assays for linkage disruption, we show first that yafN is an essential gene and second that it is essential only when yafO is present. Third, yafP is not a necessary part of either the toxin or the antitoxin. Fourth, although DinB is required, the yafNOP genes are not required for stress-induced mutagenesis in the Escherichia coli Lac assay. These results imply that yafN encodes an antitoxin that protects cells against a yafO-encoded toxin and show a protein-based TA system upregulated by the SOS response.
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030-3411, USA.
authors.forename: Larissa A
authors.initials: LA
authors.lastname: Singletary
authors.forename: Janet L
authors.initials: JL
authors.lastname: Gibson
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Tanner
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: McKenzie
authors.forename: Peter L
authors.initials: PL
authors.lastname: Lee
authors.forename: Caleb
authors.initials: C
authors.lastname: Gonzalez
authors.forename: Susan M
authors.initials: SM
authors.lastname: Rosenberg
mesh_terms: D001427:Bacterial Toxins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism / Q000633:toxicity*; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D020043:Genes, Essential; D050296:Microbial Viability; D013014:SOS Response, Genetics
chemical_list: D001427:Bacterial Toxins; D029968:Escherichia coli Proteins; C545721:YafN protein, E coli; C544331:YafO protein, E coli