Pycsar (pyrimidine cyclase system for antiphage resistance) provides immunity against bacteriophage and consists of a pyrimidine cyclase (PycC), which synthesizes cyclic nucleotides in response to infection, and an effector protein. Cyclic nucleotides serve as specific second messenger signals, which activate the adjacent effector, leading to bacterial cell death and abortive phage infection [1]. This family represents the effector protein from Pycsar system.

1: Cyclic CMP and cyclic UMP mediate bacterial immunity against phages. Tal N, Morehouse BR, Millman A, Stokar-Avihail A, Avraham C, Fedorenko T, Yirmiya E, Herbst E, Brandis A, Mehlman T, Oppenheimer-Shaanan Y, Keszei AFA, Shao S, Amitai G, Kranzusch PJ, Sorek R; Cell. 2021;184:5728-5739. PMID:34644530