Studies of the repressor (BlaI) of beta-lactamase synthesis in Staphylococcus aureus

Mol Microbiol. 1997 Jun;24(5):1025-37. doi: 10.1046/j.1365-2958.1997.4051770.x.


Purified BlaI, the putative repressor of the beta-lactamase operon in Staphylococcus aureus, binds specifically to two regions of dyad symmetry (operators) located in the blaZ-blaR1 intergenic region. BlaI binds with similar affinity to the two regions and to the related sequence upstream of the mec gene found in methicillin-resistant strains of S. aureus, providing physical evidence for the cross-talk previously observed between these systems. A change from a lysine in the N-terminus of BlaI to an alanine or deletion of the C-terminal 23 amino acids severely reduces its DNA-binding ability, demonstrating the functional importance of both the N- and C-termini. An operator DNA-protein complex observed with crude cell lysates from repressed cells, indistinguishable from that observed with purified BlaI, was eliminated by induction of the beta-lactamase operon. Furthermore, BlaI is proteolytically cleaved in response to the addition of inducer in a blaR1-dependent manner, providing primary evidence for the molecular basis of induction. Thus, BlaI is shown to be the repressor of the beta-lactamase system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Binding Sites
  • DNA, Bacterial
  • DNA-Binding Proteins / biosynthesis*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Endopeptidases / metabolism
  • Gene Expression Regulation, Bacterial
  • Molecular Sequence Data
  • Promoter Regions, Genetic
  • Repressor Proteins / biosynthesis*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / metabolism*
  • beta-Lactamase Inhibitors
  • beta-Lactamases / biosynthesis*


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Repressor Proteins
  • beta-Lactamase Inhibitors
  • Endopeptidases
  • beta-Lactamases