Evolution of an inducible penicillin-target protein in methicillin-resistant Staphylococcus aureus by gene fusion

A new β-lactam-inducible penicillin-binding protein (PBP) that has extremely low affinity to penicillin and most other β-lactam antibiotics has been widely found in highly, β-lactam(methicillin)-resistant Staphylococcus aureus (MRSA). The gene for this protein was sequenced and the nucleotide sequence in its promoter and close upstream area was found to show close similarity with that of staphylococcal penicillinase, while the amino acid sequence over a wide range of the molecule was found to be similar to those of two PBPs of Escherichia coli, the shape-determining protein (PBP 2) and septum-forming one (PBP 3). Probably the MRSA PBP ( M r 76462) evolved by recombination of two genes: an inducible type I penicillinase gene and a PBP gene of a bacterium, causing the formation of a β-lactam-inducible MRSA PBP.