title: The rifampicin-inducible genes srnB from F and pnd from R483 are regulated by antisense RNAs and mediate plasmid maintenance by killing of plasmid-free segregants.
abstract: The gene systems srnB of plasmid F and pnd of plasmid R483 were discovered because of their induction by rifampicin. Induction caused membrane damage, RNase I influx, degradation of stable RNA and, consequently, cell killing. We show here that the srnB and pnd systems mediate efficient stabilization of a mini-R1 test-plasmid. We also show that the killer genes srnB' and pndA are regulated by antisense RNAs, and that the srnC- and pndB-encoded antisense RNAs, denoted SrnC- and PndB-RNAs, are unstable molecules of approximately 60 nucleotides. The srnB and pndA mRNAs were found to be very stable. The differential decay rates of the inhibitory antisense RNAs and the killer-gene-encoding mRNAs explain the induction of these gene systems by rifampicin. Furthermore, the observed plasmid-stabilization phenotype associated with the srnB and pnd systems is a consequence of this differential RNA decay: the newborn plasmid-free cells inherit the stable mRNAs, which, after decay of the unstable antisense RNAs, are translated into killer proteins, thus leading to selective killing of the plasmid-free segregants. Thus our observations lead us to conclude that the F srnB and R483 pnd systems are phenotypically indistinguishable from the R1 hok/sok system, despite a 50% dissimilarity at the level of DNA sequence.
authors.affiliation: Department of Molecular Biology, Odense University, Denmark.
authors.forename: A K
authors.initials: AK
authors.lastname: Nielsen
authors.forename: P
authors.initials: P
authors.lastname: Thorsted
authors.forename: T
authors.initials: T
authors.lastname: Thisted
authors.forename: E G
authors.initials: EG
authors.lastname: Wagner
authors.forename: K
authors.initials: K
authors.lastname: Gerdes
mesh_terms: D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D004261:DNA Replication / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005144:F Factor / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics*; D005804:Genes, Lethal / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011815:R Factors / Q000235:genetics*; D015347:RNA Probes / Q000235:genetics; D016372:RNA, Antisense / Q000235:genetics*; D012329:RNA, Bacterial / Q000235:genetics; D012293:Rifampin / Q000494:pharmacology
chemical_list: D015347:RNA Probes; D016372:RNA, Antisense; D012329:RNA, Bacterial; D012293:Rifampin