This domain is present is the N-terminal region of a group of polymorphic toxin proteins in bacteria. It is predicted to use Type VII secretion pathway to mediate export of bacterial toxins [1].

1: A novel immunity system for bacterial nucleic acid degrading toxins and its recruitment in various eukaryotic and DNA viral systems. Zhang D, Iyer LM, Aravind L; Nucleic Acids Res. 2011;39:4532-4552. PMID:21306995