Characterization of the DNA Binding Domain of StbA, A Key Protein of A New Type of DNA Segregation System

J Mol Biol. 2022 Oct 15;434(19):167752. doi: 10.1016/j.jmb.2022.167752. Epub 2022 Jul 19.


Low-copy-number plasmids require sophisticated genetic devices to achieve efficient segregation of plasmid copies during cell division. Plasmid R388 uses a unique segregation mechanism, based on StbA, a small multifunctional protein. StbA is the key protein in a segregation system not involving a plasmid-encoded NTPase partner, it regulates the expression of several plasmid operons, and it is the main regulator of plasmid conjugation. The mechanisms by which StbA, together with the centromere-like sequence stbS, achieves segregation, is largely uncharacterized. To better understand the molecular basis of R388 segregation, we determined the crystal structure of the conserved N-terminal domain of StbA to 1.9 Å resolution. It folds into an HTH DNA-binding domain, structurally related to that of the PadR subfamily II of transcriptional regulators. StbA is organized in two domains. Its N-terminal domain carries the specific stbS DNA binding activity. A truncated version of StbA, deleted of its C-terminal domain, displays only partial activities in vivo, indicating that the non-conserved C-terminal domain is required for efficient segregation and subcellular plasmid positioning. The structure of StbA DNA-binding domain also provides some insight into how StbA monomers cooperate to repress transcription by binding to the stbDR and to form the segregation complex with stbS.

Keywords: DNA segregation; bacterial conjugation; helix-turn-helix; plasmid; transcription factor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins* / chemistry
  • Chromosome Segregation*
  • DNA / chemistry
  • DNA / metabolism
  • Nucleoside-Triphosphatase* / chemistry
  • Nucleoside-Triphosphatase* / metabolism
  • Operon
  • Plasmids* / genetics
  • Protein Domains


  • Bacterial Proteins
  • chromosome partition proteins, bacterial
  • DNA
  • Nucleoside-Triphosphatase