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). A cyclic nucleotide-activated dsDNase. In the presence of 3',3',3'-cyclic AMP-AMP-AMP (cAAA) and to a lesser extent cyclic-di-AMP (c-di-AMP), endonucleolytically degrades dsDNA (Probable). Binds one cAAA in a pocket on one surface of the trimer; cAAA binding promotes hexamerization which is probably necessary for nuclease activation (PubMed:31932164). The nuclease digests dsDNA to about 50 bp lengths. DNA has been modeled to contact a pair of juxtaposed active sites (one from each layer of the hexamer), accounting for cleavage on both strands (By similarity). Activated by cAAA and to a lesser extent cAA; both cyclic nucleotides are products of its cognate CD-NTase. Cyclic nucleotide binding causes hexamerization. Self-oligomerizes (PubMed:31932165). Forms homotrimers; in the presence of cAAA the trimers associate face-to-face to form homohexamers. The 2 cAAA-binding sites are on the exterior of the hexamer at the three-way junction, there are maximally 2 cyclic nucleotides per hexamer (PubMed:31932164). Second messenger binding causes a series of shifts that enclose the cAAA molecule. Belongs to the NucC endonuclease family.