Identification of the pac promoter from Kluyvera citrophila

The nucleotide sequence of the 5'-terminal region of the pac gene encoding the penicillin G acylase from Kluyvera citrophila ATCC 21285 has been determined. The transcriptional start site has been identified by primer extension analysis in a different position to that previously found for the homologous pac gene of Escherichia coli W ATCC 11105. Two nucleotide changes in the -35 box appear to be responsible of the promoter displacement in K. citrophila. A putative upstream promoter element (A+T-rich enhancer sequence) and a binding site for the cAMP receptor protein (CRP) were located upstream of the -35 box. Transcriptional lacZ and cat fusions demonstrated that pac expression was subjected to catabolite repression mediated by cAMP and its receptor protein. Remarkably, phenylacetic acid which is a potent inducer of the penicillin G acylase from E. coli, was only able to cause a significant induction of the pac expression in CRP+ cells cultured in the presence of glucose, suggesting that this effect is CRP-dependent.