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 I-D(GG) CBASS system (PubMed:32839535). Cyclic dinucleotide synthase that catalyzes the synthesis of c-di-GMP, has no activity with other NTP substrates. 2 GTP = cyclic di-3',5'-guanylate + 2 diphosphate Bacteria with this enzyme do not have other c-di-GMP synthase enzymes (no GGDEF or EAL-domain containing proteins), suggesting this second messenger has been co-opted for CBASS signaling via STING activation. Belongs to the CD-NTase family.