A Common System Controls the Induction of Very Different Genes

Abstract

Among the Enterobacteriaceae, Proteus vulgaris is exceptional in the inducible production of a 29‐kDa β‐lactamase (cefuroximase) with an unusually high activity towards the β‐lactamase‐stable oximino‐cephalosporins (e.g. cefuroxime and cefotaxime). Sequencing of the corresponding gene, cumA, showed that the derived CumA β‐lactamase belonged to the molecular class A. The structural gene was under the direct control of gene cumR, which was transcribed backwards and whose initiation codon was 165 bp away from that of the β‐lactamase gene. This resembled the arrangement of structural and regulator genes ampC and ampR of the 39‐kDa molecular‐class‐C β‐lactamase AmpC present in many enterobacteria. Moreover, cloned genes ampD and ampG for negative modulation and signal transduction of AmpC β‐lactamase induction, respectively, were also able to restore constitutively CumA overproducing and non‐inducible P. vulgaris mutants to the inducible, wild‐type phenotype. The results indicate that controls of the induction phenomena are equivalent for the CumA and AmpC β‐lactamase. Very different structural genes can thus be under the control of identical systems.