SUMMARY: In 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 recombination either into bacteriophage λ or low-copy-number plasmids, or directly on the chromosome at the locus. The fusions were used in physiological experiments as probes to study transcriptional and translational controls of 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 expression. In addition it was observed that concomitant with a severe slackening of growth rate, specific to the growth of strains in rich medium, 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 message was very weak when compared to transcription (the mRNA level was the same in protein and operon fusions).


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