The DisA protein is a bacterial checkpoint protein that dimerises into an octameric complex. The protein consists of three distinct domains. This domain is the first and is a globular, nucleotide-binding region; the next 146-289 residues constitute the DisA-linker family, Pfam:PF10635, that consists of an elongated bundle of three alpha helices (alpha-6, alpha-10, and alpha-11), one side of which carries an additional three helices (alpha7-9), which thus forms a spine like-linker between domains 1 and 3. The C-terminal residues, of domain 3, are represented by family HHH, Pfam:PF00633, the specific DNA-binding domain. The octameric complex thus has structurally linked nucleotide-binding and DNA-binding HhH domains and the nucleotide-binding domains are bound to a cyclic di-adenosine phosphate such that DisA is a specific di-adenylate cyclase. This N-terminal domain has been identified as a diadenylate cyclase (DAC) responsible for producing c-di-AMP from two molecules of ATP [1]. The di-adenylate cyclase activity is strongly suppressed by binding to branched DNA, but not to duplex or single-stranded DNA, suggesting a role for DisA as a monitor of the presence of stalled replication forks or recombination intermediates via DNA structure-modulated c-di-AMP synthesis [2].

1: Cyclic di-AMP, a second messenger of primary importance: tertiary structures and binding mechanisms. He J, Yin W, Galperin MY, Chou SH; Nucleic Acids Res. 2020 Feb 25. pii: 5755; [Epub ahead of print] PMID:32095817

2: Structural biochemistry of a bacterial checkpoint protein reveals diadenylate cyclase activity regulated by DNA recombination intermediates. Witte G, Hartung S, Buttner K, Hopfner KP; Mol Cell. 2008;30:167-178. PMID:18439896