Mechanism of post-segregational kilting by the hok/sok system of plasmid R1: sok antisense RNA regulates formation of a hok mRNA species correlated with killingof plasmid-free cells

K. Gerdes, T. Thisted, Jan Martinussen

Research output: Contribution to journalJournal articleResearchpeer-review


The hok/sok system of plasmid R1, which mediates plasmid stabilization via killing of plasmid-free segregants, encodes two genes: hok and sok. The hok gene product is a potent cell-killing protein. The expression of hok is regulated post-transcriptionally by the sok gene-encoded repressor, an antisense RNA complementary to the hok mRNA leader region. We show here that the hok mRNA is very stable, while the sok RNA decays rapidly. We also observe a new hok mRNA species which is 70 nucleotides shorter in the 3'-end than the full-length hok transcript. The appearance of the truncated hok mRNA was found to be regulated by the sok antisense RNA. Furthermore, the presence of the truncated hok mRNA was found to be correlated with efficient expression of the Hok protein. On the basis of these findings, we propose an extended model in order to explain the killing of plasmid-free segregants by the hok/sok system.
Original languageEnglish
JournalMolecular Microbiology
Issue number11
Pages (from-to)1807-1818
Number of pages12
Publication statusPublished - 1990
Externally publishedYes


  • Base Sequence
  • Escherichia coli
  • Gene Expression Regulation, Bacterial
  • Genes, Bacterial
  • Genes, Regulator
  • Molecular Sequence Data
  • Plasmids
  • RNA, Antisense
  • RNA, Bacterial
  • RNA, Messenger
  • Transcription, Genetic
  • Facultatively Anaerobic Gram-Negative Rods Eubacteria Bacteria Microorganisms (Bacteria, Eubacteria, Microorganisms) - Enterobacteriaceae [06702]
  • 10062, Biochemistry studies - Nucleic acids, purines and pyrimidines
  • 10064, Biochemistry studies - Proteins, peptides and amino acids
  • 10300, Replication, transcription, translation
  • 10506, Biophysics - Molecular properties and macromolecules
  • 13012, Metabolism - Proteins, peptides and amino acids
  • 13014, Metabolism - Nucleic acids, purines and pyrimidines
  • 31000, Physiology and biochemistry of bacteria
  • 31500, Genetics of bacteria and viruses
  • Biochemistry and Molecular Biophysics
  • Genetics
  • Metabolism
  • Molecular Genetics
  • Physiology

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