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-A(UA) CBASS system (PubMed:32839535). Cyclic dinucleotide synthase that catalyzes the synthesis of 3',3'-cyclic UMP-AMP (cUMP-AMP) from UTP and ATP, a second messenger for cell signal transduction. Controls the activity of cUAMP-activated phospholipase CapE, a patatin-like lipase that is a direct cUMP-AMP receptor encoded in the cdnE operon. ATP + UTP = 3',3'-cUAMP + 2 diphosphate Binds 1 Mg(2+) ion per subunit. Optimum pH is 9.4. This is a complex CBASS locus with the loci capE-cdnE-probable diadenylate cyclase-capV-dcnV1-cap2-cap3. Belongs to the CD-NTase family. E01 subfamily.