Small, rapidly-evolving domain predicted to possess a compact, four-helix structure. Along with a gene encoding a TPR repeat region fused to a CASPASE domain and a gene encoding the CATRA module (CATRA-N+CATRA-C) C-terminally fused to a diverse range of conflict effector domains, forms the three gene island making up the CATRA conflict systems. Plays a possible inhibitory role in the CATRA system which is relieved upon sensing of an invasive molecule or is directly cleaved by the CASPASE domain.

1: Identification of Uncharacterized Components of Prokaryotic Immune Systems and Their Diverse Eukaryotic Reformulations. Burroughs AM, Aravind L; J Bacteriol. 2020; [Epub ahead of print] PMID:32868406