A mutant transcription factor that is activated by 3':5'-cyclic guanosine monophosphate

We report here the isolation of an extragenic suppressor of a promoter mutation in the lactose operon of Escherichia coli. Genetic data have indicated that the suppressor of the P(-) mutation maps in the structural gene for the transcription factor catabolite activator protein. Biochemical studies suggest that the mutant molecules of catabolite activator protein are altered in such a way that they are activated by 3':5'-cyclic GMP in addition to their normal effector, 3':5'-cyclic AMP.