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. Binds ATP or AMP depending on its partner protein, and probably catalytic cycle. Protects E.coli strain JP313 against bacteriophage lambda cI- infection. When the cdnC-cap7-cap6-nucC operon is transformed into a susceptible strain it confers bacteriophage immunity. Mutations in the sensor (Cap7 also called HORMA) or effector proteins (CdnC, NucC) but not the disassembly protein (Cap6 also called Trip13) no longer confer immunity. The presence of the intact operon leads to culture collapse and cell death, which occurs before the phage has finished its replication cycle, thus protecting non-infected bacteria by aborting the phage infection and preventing its propagation. 3 ATP = 2',3',3'-c-tri-AMP + 3 diphosphate 2 ATP = 3',3'-c-di-AMP + 2 diphosphate The 2:2 CdnC:Cap7 (Cap7 is also called HORMA) complex is activated for cAAA synthesis by long dsDNA, but not 40 bp dsDNA or ssDNA; the 1:1 complex is inactive in vitro. The 2:2:DNA complex is deactivated by Cap6 (also called Trip13). Forms complexes with Cap7 with 1:1 and 2:2 stoichimetry, and a 1:1:6 CdnC:Cap7:Cap6 complex. In the disassembly complex (PDB:6P8V) Cap6 (also called Trip13) crystallizes as a right-handed spiral; the top 4 subunits bind ATP while the bottom 2 do not. A CdnC monomer lies along the surface of the hexamer at the interface of subunits 5 and 6, with Cap7 (also called HORMA) at its tip, over the central hexamer pore. The N-terminus of Cap7 extends into the pore, contacting 5/6 Cap6 subunits. Belongs to the CD-NTase family. A01 subfamily. Extended N-terminus.