Participates in a DNA-damage check-point. DisA forms globular foci that rapidly scan along the chromosomes searching for lesions. Has diadenylate cyclase activity, catalyzing the condensation of 2 ATP molecules into cyclic di-AMP (c-di-AMP) (PubMed:18439896, PubMed:26014055). c-di-AMP likely acts as a signaling molecule that may couple DNA integrity with a cellular process. This rate-limiting step is the accessibility of the active site; mutating the possible exit tunnel (residues 128-130) increases product 2-fold despite Arg-130 being important for ATP-binding (PubMed:26014055). Does not convert GTP to c-di-GMP (PubMed:18439896). 2 ATP = 3',3'-c-di-AMP + 2 diphosphate Crystallized with Mn(2+) to trap in the pre-reaction state. Inhibited by 3'-dATP. Homooctamer. Consists of three domains: an N-terminal globular domain with diadenylate-cyclase (DAC) activity, a central helical domain and a C-terminal DNA-binding domain. Belongs to the DisA family.