Cyclic adenosine 3',5'-monophosphate-mediated hyperinduction of araBAD and lacZYA expression in a crp mutant of Escherichia coli K-12.

A spontaneous lac+ revertant of an adenylate cyclase deletion strain of Escherichia coli K-12 was isolated and characterized. This revertant, designated strain KC20, exhibited a pleiotropic suppression of the adenylate cyclase defect, with the crp locus being the site of the suppressor mutation. Cyclic adenosine 3',5'-monophosphate at an exogenous concentration of 1 mM severely inhibited the growth of strain KC20 in minimal media. Lower concentrations of the cyclic nucleotide elicited less pronounced effects. Studies on araBAD and lacZYA expression showed that cyclic adenosine 3',5'-monophosphate elicited an initial dose-dependent hyperinduction of these systems. Hyperinduction of araBAD, in L-arabinose grown cultures of strain KC20, resulted in accumulation of inhibitory concentrations of methylglyoxal. Hyperinduction of lacZYA in lactose-grown cultures of strain KC20 did not result in any such methylglyoxal production.