Pycsar (pyrimidine cyclase system for antiphage resistance) provides immunity against bacteriophage. The pyrimidine cyclase (PycC) synthesizes cyclic nucleotides in response to infection; these serve as specific second messenger signals. The signals activate the adjacent effector, leading to bacterial cell death and abortive phage infection. A clade C Pycsar system. The pyrimidine cyclase gene of a two-gene Pycsar system, weakly generates cyclic UMP (cUMP) from UTP, has little to no activity on ATP, CTP or GTP (PubMed:34644530). Expression of this and adjacent effector TpPycTM (AC A0A1T4LJG1) probably confers resistance to bacteriophage. The genes are probably only expressed in response to bacteriophage infection (Probable). UTP = 3',5'-cyclic UMP + diphosphate Homodimer. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family. Pyrimidine cyclase subfamily.