Small RNA-based feedforward loop with AND-gate logic regulates extrachromosomal DNA transfer in Salmonella

Proc Natl Acad Sci U S A. 2015 Aug 25;112(34):E4772-81. doi: 10.1073/pnas.1507825112. Epub 2015 Aug 11.

Abstract

Horizontal gene transfer via plasmid conjugation is a major driving force in microbial evolution but constitutes a complex process that requires synchronization with the physiological state of the host bacteria. Although several host transcription factors are known to regulate plasmid-borne transfer genes, RNA-based regulatory circuits for host-plasmid communication remain unknown. We describe a posttranscriptional mechanism whereby the Hfq-dependent small RNA, RprA, inhibits transfer of pSLT, the virulence plasmid of Salmonella enterica. RprA employs two separate seed-pairing domains to activate the mRNAs of both the sigma-factor σ(S) and the RicI protein, a previously uncharacterized membrane protein here shown to inhibit conjugation. Transcription of ricI requires σ(S) and, together, RprA and σ(S) orchestrate a coherent feedforward loop with AND-gate logic to tightly control the activation of RicI synthesis. RicI interacts with the conjugation apparatus protein TraV and limits plasmid transfer under membrane-damaging conditions. To our knowledge, this study reports the first small RNA-controlled feedforward loop relying on posttranscriptional activation of two independent targets and an unexpected role of the conserved RprA small RNA in controlling extrachromosomal DNA transfer.

Keywords: Hfq; RprA; feedforward control; plasmid conjugation; sRNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Chromosomes, Bacterial*
  • DNA, Bacterial / genetics*
  • Molecular Sequence Data
  • RNA, Bacterial / genetics*
  • Salmonella / genetics*
  • Sequence Homology, Nucleic Acid

Substances

  • DNA, Bacterial
  • RNA, Bacterial

Associated data

  • GEO/GSE67187