Regulation of adenylate cyclase synthesis in Escherichia coli: Studies with cya-lac operon and protein fusion strains

Abstract

The authors have isolated cya-lac operon and protein fusions in E. coli K-12, and they used these to study the regulation of cya, the structural gene for adenylate cyclase. Data obtained from these fusion strains suggest that neither cyclic AMP (cAMP) nor the cAMP receptor protein plays a major role in transcriptional or translational regulation of cya expression. Modulation of intracellular cAMP concentrations elicited only weak repression of cya-lac fusion activity under conditions of high intracellular cAMP, relative to fusion activity under conditions of low intracellular cAMP. The functional cAMP receptor protein was required for this effect. Incorporation of Δcrp into cya-lac fusion strains did not affect fusion expressions in glucose-grown cells as compared with similarly cultured isogenic crp+ strains. Furthermore, 20 independently obtained mutants derived from a cya-lacZ protein fusion strain exhibiting a weak Lac+ phenotype were isolated, and it was determined that the mutants had β-galactosidase activities ranging from 2- to 77-fold greater than those of the parental strain. None of the mutations responsible for this increase in fusion activity map in the crp locus. The authors used these mutants to aid in the identification of a 160,000 dalton cya-lacZ hybrid protein. Finally, chromosome mobilization experiments, using cya-lac fusion strains, allowed them to infer a clockwise direction of transcription for the cya gene relative to the standard E. coli genetic map.