Comprehensive analysis of IncC plasmid conjugation identifies a crucial role for the transcriptional regulator AcaB

Nat Microbiol. 2020 Nov;5(11):1340-1348. doi: 10.1038/s41564-020-0775-0. Epub 2020 Aug 17.


The IncC family of broad-host-range plasmids enables the spread of antibiotic resistance genes among human enteric pathogens1-3. Although aspects of IncC plasmid conjugation have been well studied4-9, many roles of conjugation genes have been assigned based solely on sequence similarity. We applied hypersaturated transposon mutagenesis and transposon-directed insertion-site sequencing to determine the set of genes required for IncC conjugation. We identified 27 conjugation genes, comprising 19 that were previously identified (including two regulatory genes, acaDC) and eight not previously associated with conjugation. We show that one previously unknown gene, acaB, encodes a transcriptional regulator that has a crucial role in the regulation of IncC conjugation. AcaB binds upstream of the acaDC promoter to increase acaDC transcription; in turn, AcaDC activates the transcription of IncC conjugation genes. We solved the crystal structure of AcaB at 2.9-Å resolution and used this to guide functional analyses that reveal how AcaB binds to DNA. This improved understanding of IncC conjugation provides a basis for the development of new approaches to reduce the spread of these multi-drug-resistance plasmids.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Conjugation, Genetic / genetics*
  • Crystallography, X-Ray
  • Drug Resistance, Multiple, Bacterial
  • Escherichia coli / genetics
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Mutagenesis
  • Mutation
  • Plasmids / genetics*
  • Promoter Regions, Genetic
  • Protein Structure, Secondary
  • Trans-Activators / chemistry
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcription, Genetic


  • AcaB protein, E coli
  • Escherichia coli Proteins
  • Trans-Activators
  • Transcription Factors