Evidence for negative control of cya transcription by cAMP and cAMP receptor protein in intact Escherichia coli cells.

The transcriptional regulation of cya by cAMP and its receptor protein (CRP) has been studied by S1 nuclease and RNA dot blot assays. The crp- Escherichia coli cells were shown to produce about 5-fold more cya mRNA than do the wild type cells. The effect of cAMP and CRP on the cya transcription was directly examined by introducing a crp plasmid into the cells and/or by adding cAMP exogenously. The levels of cya mRNA in crp+ cells decreased with increasing concentrations of cAMP in the growth medium. The repressive effect of cAMP on cya transcription was strongly enhanced in cells carrying a multicopy crp plasmid. These results indicate that the cya transcription is negatively regulated by cAMP-CRP complex in intact cells.