A predicted immunity protein with a mostly alpha-helical fold and conserved arginine and phenylalanine residues. Proteins containing this domain are present in bacterial polymorphic toxin systems as an immediate gene neighbour of the toxin gene, which usually contains toxin domains of the Ntox48 family [1]. This domain is often fused to the Imm72 immunity domain.

1: Polymorphic toxin systems: comprehensive characterization of trafficking modes, processing, mechanisms of action, immunity and ecology using comparative genomics. Zhang D, de Souza RF, Anantharaman V, Iyer LM, Aravind L; Biol Direct. 2012;7:18. PMID:22731697