This domain is found in the C terminus of N(4)-bis(aminopropyl)spermidine synthase (EC:2.5.1.128, also known as Branched-chain polyamine synthase A, BpsA) from hyperthermophiles [1] and in uncharacterised proteins from bacteria and archaea.

1: Identification of a novel aminopropyltransferase involved in the synthesis of branched-chain polyamines in hyperthermophiles. Okada K, Hidese R, Fukuda W, Niitsu M, Takao K, Horai Y, Umezawa N, Higuchi T, Oshima T, Yoshikawa Y, Imanaka T, Fujiwara S; J Bacteriol. 2014;196:1866-1876. PMID:24610711