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 (Probable). A type II-C CBASS system (PubMed:32839535). Probably in the presence of its endogenous cyclic nucleotide (synthesized by the cognate CD-NTase protein in the CBASS operon), or of 2',3',3'-cyclic AMP-AMP-AMP (cAAA) synthesized by Acinetobacter sp. ATCC 27244, endonucleolytically degrades dsDNA in a non-sequence specific manner. It is not activated by other cyclic nucleotides. DNase activity is activated upon ligand binding. A monomer in the absence of cAAA, in its presence it forms oligomers. Part of the CBASS operon consisting of cdnD-cap2-cap3-cap4. The cyclic nucleotide ligand binds in the C-terminal SAVED domain. Belongs to the Cap4 nuclease family.