Regulation of penicillin G acylase gene expression in Escherichia coli by repressor PaaX and the cAMP-cAMP receptor protein complex

The pga gene of Escherichia coli W ATCC11105 encodes a penicillin G acylase whose expression is regulated at both the transcriptional and post-transcriptional level. In this work we have shown that PaaX is the repressor of pga expression, and we have identified its binding consensus as TGATTC(N-27)GAATCA. We conclude that the process of PAA induction actually involves relief of pga from repression by PaaX. Other features of the pga promoter have also been characterized. (i) It has a native class III cAMP-receptor protein (CRP)-dependent promoter with two CRP-binding sites. (ii) The downstream CRP-binding site II has higher affinity. (iii) Binding of cAMP-CRP to both sites (I + II) is required for maximal expression. We have also shown that the PaaX-binding site overlaps with the CRP-binding site I. This implies that PaaX and the cAMP-CRP compete for binding to the region around the CRP-binding site I and therefore have antagonistic effects on pga expression.