[Study of the expression of the cya gene in Escherichia coli K12 on a model of the hybrid cya-lac operon].

Bacteriophage Mud1 (Ap, lac) was used to construct the cya-lac operon fusion in Escherichia coli chromosome. The maximal cya expression was observed by measuring the levels of beta-galactosidase in the strains lacking the cAMP. The inhibition of cya transcription was proportional either to the amount of cAMP added or to the copy number of cya gene in the cell. Functional cAMP receptor protein (CRP) was necessary for the effect. The cya gene expression was low in cAMP-independent crp mutant even in the absence of the cAMP.