This domain is found mostly in bacteria. It is found at the N-terminal of Shedu protein SduA, the only component of antiviral defense system Shedu. Expression of Shedu in B.subtilis (strain BEST7003) confers resistance to phages phi105, phi29, rho14 and to a lesser extent to SPP1 [1].

1: Systematic discovery of antiphage defense systems in the microbial pangenome. Doron S, Melamed S, Ofir G, Leavitt A, Lopatina A, Keren M, Amitai G, Sorek R; Science. 2018; [Epub ahead of print] PMID:29371424