Agr-independent regulation of fibronectin-binding protein(s) by the regulatory locus sar in Staphylococcus aureus

Mol Microbiol. 2000 Apr;36(1):230-43. doi: 10.1046/j.1365-2958.2000.01853.x.


Fibronectin-binding proteins (FnBPs) are thought to be important for the attachment of Staphylococcus aureus during infection. The regulation of the genes fnbA and fnbB by the global regulatory loci sar and agr was examined using site-specific regulatory mutants of S. aureus strain Newman. The results from binding assays using both aqueous and solid-phase fibronectin as well as ligand blotting with biotinylated fibronectin showed that the expression of FnBPA is enhanced in the agr mutant but inhibited in the sar mutant and the sar-agr double mutant. The same regulatory pattern was observed in Northern blot analysis using fnbA-specific probes. The introduction of sar on a multicopy plasmid increased the already enhanced fnbA transcription of the agr mutant. FnBPB was not detectable by ligand blotting and the fnbB promoter activity in promoter fusion assays was not affected by either sar or agr. The sequence encompassing ORF3 located upstream of sarA was found to be essential for the activation of fnbA transcription. We hypothesize that this sequence may modulate SarA expression and/or activity on the post-transcriptional level. Gel shift assays demonstrated that SarA binds to the fnbA promoter fragments, probably as a dimer. DNase I footprinting assays with SarA revealed a protected area of 102 bp upstream of fnbA.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adhesins, Bacterial*
  • Bacterial Adhesion / genetics*
  • Bacterial Proteins / biosynthesis
  • Bacterial Proteins / genetics*
  • Base Sequence
  • Binding Sites
  • Carrier Proteins / genetics*
  • Dimerization
  • Fibronectins / metabolism
  • Gene Expression Regulation, Bacterial
  • Genes, Reporter
  • Green Fluorescent Proteins
  • Hemolysin Proteins / biosynthesis
  • Hemolysin Proteins / genetics
  • Hemolysis
  • Ligands
  • Luminescent Proteins / genetics
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Protein Binding
  • Staphylococcal Protein A / biosynthesis
  • Staphylococcal Protein A / genetics
  • Staphylococcus aureus / genetics*
  • Staphylococcus aureus / pathogenicity
  • Trans-Activators*
  • Transcription Factors / genetics*
  • Transcriptional Activation


  • Adhesins, Bacterial
  • Agr protein, Staphylococcus aureus
  • Bacterial Proteins
  • Carrier Proteins
  • Fibronectins
  • Hemolysin Proteins
  • Ligands
  • Luminescent Proteins
  • SarA protein, bacterial
  • Staphylococcal Protein A
  • Trans-Activators
  • Transcription Factors
  • fibronectin-binding proteins, bacterial
  • Green Fluorescent Proteins
  • delta hemolysin protein, Staphylococcus aureus