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 effector gene of a two-gene Pycsar system. Expression of this and adjacent uridylate cyclase TpPycC (AC A0A1T4LJ54) probably confers resistance to bacteriophage. The genes are probably only expressed in response to bacteriophage infection. Probably only responds to cUMP (produced by its cognate NTP cyclase), acts by impairing membrane integrity.