Aspects of the regulation of adenylate cyclase synthesis in Escherichia coli K12.

In Escherichia coli K12 expression of the adenylate cyclase gene is subject to multiple controls. In order to gain understanding of the regulation of adenylate cyclase synthesis, operon and protein fusions were constructed by in vitro recombination either into bacteriophage lambda or low-copy-number plasmids, or directly on the chromosome at the cya locus. The fusions were used in physiological experiments as probes to study transcriptional and translational controls of cya expression. It was found that adenylate cyclase synthesis was insensitive to glucose effects. As already described by other workers, the CAP-cAMP complex had a moderate negative control on cya expression. In addition it was observed that concomitant with a severe slackening of growth rate, specific to the growth of cya strains in rich medium, cya expression was considerably enhanced. This increase of adenylate cyclase synthesis did not appear to be directly dependent on the presence of a functional cAMP receptor (CAP), and seemed to be controlled at the level of transcription. Finally, translation of the cya message was very weak when compared to cya transcription (the mRNA level was the same in protein and operon fusions.