Mutations affecting the diadenylate cyclase CdaA. TM, transmembrane region; CC, coiled-coil domain; DAC, diadenylate cyclase domain; #, DGA and RHR active site motifs; SD, Shine-Dalgarno sequence (the first G of the sequence is replaced by a T in the suppressor mutant GP2134); *, frameshift mutations (both mutations result in the production of inactive truncated proteins); △, C-terminal deletion.