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(GA) CBASS system (PubMed:32839535). Protects E.coli against phage P1 and T2 infection. When the 4 gene operon capV-dncV-cap2-cap3 is introduced in E.coli MG1655 there is about 100-fold protection against phages P1 and T2 (PubMed:31533127). Protects E.coli against phage T2 infection. When the CBASS operon (capV-dcnV-cap2-cap3) is introduced in E.coli MG1655 there is a more than 10(3) decrease in the efficiency of T2 plaque formation. Protects 100-fold against phage T5, offers no protection against T7 (PubMed:32544385). Part of the CBASS operon consisting of capV-dncV-cap2-cap3. In the C-terminal section; belongs to the HesA/MoeB/ThiF family.