This is a STING sensor domain found in certain prokaryotic nucleotide-activated effector conflict systems. Binding to a nucleotide activates fused effector proteins in conflict response against invasive elements. Certain versions in prokaryotes may additionally regulate bacterial ion channels. Transferred to eukaryotes on multiple occasions, representatives observed are in animal-choanoflagellate, haptophyte/stramenopile, and fungal lineages [1].

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