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(GA) CBASS system (PubMed:32839535). Catalyzes the synthesis of 3'3'-cyclic GMP-AMP (3'3'-cGAMP) from GTP and ATP, a second messenger in cell signal transduction. Is also able to produce c-di-AMP and c-di-GMP from ATP and GTP, respectively; however, 3'3'-cGAMP is the dominant molecule produced by DncV in vivo, contrary to the 2'3'-cGAMP produced by eukaryotes. By producing cGAMP, down-regulates csgD expression and expression of flagellum regulon genes, which leads to the down-regulation of rdar biofilm formation and flagellum-mediated swimming and swarming motility in a temperature-dependent manner (PubMed:30837338). Controls the activity of cGAMP-activated phospholipase CapV, a patatin-like lipase that is a direct 3',3'-cGAMP receptor encoded in the dncV operon (By similarity). ATP + GTP = 3',3'-cGAMP + 2 diphosphate Binds 1 Mg(2+) ion per subunit. Deletion of dncV incrementally, but significantly, enhances swimming and swarming motility compared to the ECOR31 wild-type. It also enhances biofilm formation on abiotic surfaces after 48 hours of development. This is a complex CBASS locus with the loci capE-cdnE-probable diadenylate cyclase-capV-dcnV1-cap2-cap3. Belongs to the CD-NTase family. A01 subfamily.