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 II-C(AAAA) CBASS system (PubMed:32839535). Cyclic trinucleotide synthase that catalyzes the synthesis of 2',3',3'-cyclic AMP-AMP-AMP as the major product, as well as another cyclic AMP(4) 2'-5'-linked minor product that acts as a second messenger for cell signal transduction. 3 ATP = 2',3',3'-c-tri-AMP + 3 diphosphate Binds 1 Mg(2+) ion per subunit. Part of the CBASS operon consisting of cdnD-cap2-cap3-cap4. Belongs to the CD-NTase family. D01 subfamily.