The KAP (after Kidins220/ARMS and PifA) family of predicted NTPases are sporadically distributed across a wide phylogenetic range in bacteria and in animals. Many of the prokaryotic KAP NTPases are encoded in plasmids and tend to undergo disruption to form pseudogenes. A unique feature of all eukaryotic and certain bacterial KAP NTPases is the presence of two or four transmembrane helices inserted into the P-loop NTPase domain. These transmembrane helices anchor KAP NTPases in the membrane such that the P-loop domain is located on the intracellular side [1].

1: A novel family of P-loop NTPases with an unusual phyletic distribution and transmembrane segments inserted within the NTPase domain. Aravind L, Iyer LM, Leipe DD, Koonin EV; Genome Biol 2004;5:R30. PMID:15128444