CBASS (cyclic oligonucleotide-based antiphage signaling system) provides immunity against bacteriophage. The CD-NTase protein synthesizes cyclic nucleotides in response to infection; these serve as specific second messenger signals. The signals activate a diverse range of effectors, leading to bacterial cell death and thus abortive phage infection. A type III-C(AAA) CBASS system (PubMed:32839535). Cyclic nucleotide synthase that upon activation catalyzes the synthesis of 2',3',3'-cyclic AMP-AMP-AMP (cAAA) as the major product, and c-di-AMP as a minor product at pH 8.5. At pH 7.5 also makes 3',3',3'-cyclic AMP-AMP-GMP. Binds ATP and much less well to GTP. 3 ATP = 2',3',3'-c-tri-AMP + 3 diphosphate 2 ATP + GTP = cyclic AMP-AMP-GMP + 3 diphosphate 2 ATP = 3',3'-c-di-AMP + 2 diphosphate Crystallized with and without Mg-ATP. Activated for cAAA synthesis by Cap7 (also called HORMA2) and by Cap7:Cap8 (HORMA2:HORMA3). Does not require dsDNA for activity. The CdnD:Cap7:Cap8 complex (also called CdnD:HORMA2:HORMA3) is deactivated by Cap6 (also called Trip13). Interacts individually with Cap7 and Cap8; forms CdnD:Cap7:Cap8 complexes with stoichiometries of 1:1:1 and 2:1:1. The 2 domains are closer in the ATP-bound enzyme. Belongs to the CD-NTase family. D05 subfamily.