Transcription of the speC (ornithine decarboxylase) gene of Escherichia coli is repressed by cyclic AMP and its receptor protein.

The speC gene encoding ornithine decarboxylase (ODC) in Escherichia coli is negatively regulated by cAMP and the cAMP receptor protein (CRP). In minicells transformed with the plasmid pODC bearing speC, cAMP supplementation repressed ODC synthesis. In a cell-free protein synthesizing system directed by pODC, cAMP at 10(-5) M repressed ODC synthesis by 90%. This repression required a functional CRP as cAMP failed to repress ODC synthesis in vitro in an extract prepared from a crp- strain; the addition of purified CRP to the crp- extract restored the ability of cAMP to repress ODC synthesis. In a prototroph transformed with the plasmid pCOD bearing a speC::tet chimeric gene, cAMP supplementation decreased tetracycline (Tc) resistance. In contrast, in crp- strains transformed with pCOD or pTET (TcR), cAMP supplementation did not change their Tc resistance. When a cya- strain was supplemented with 2 mM cAMP, steady state levels of ODC mRNA were repressed by 80%. However, when a isogenic crp- strain was supplemented with 2 mM cAMP, no repression of ODC mRNA was observed. These results indicate that the cAMP-CRP complex exerts negative transcriptional control of ODC synthesis as a function of the speC promoter.