This domain can be found in 5' to 3' exoribonuclease 1 (XRN1) which belong to a family of conserved enzymes in eukaryotes and have important functions in transcription, RNA metabolism, and RNA interference. Xrn1 in fungi and animals is primarily cytosolic, involved in degradation of decapped mRNAs, nonsense mediated decay, microRNA decay and is essential for proper development. The Xrn1 homolog in Drosophila, known as Pacman, is required for male fertility [1]. This entry relates to domain 2 and 3 combined which can be found in the 510-residue C-terminal extension found in XRN1 and not in XRN2/Rat1. Domain D2 is formed by two stretches of Xrn1, residues 915-960 and 1134-1151. The presence of domain (D3) is suggested based on structure. This domain is formed by residues 979-1109, in the insert of domain D2. It is suggested that domains D2-D4 may help maintain domain D1 Pfam:PF18332 in the correct conformation, thereby indirectly stabilising the conformation of the N-terminal segment Pfam:PF03159 [1].

1: Structural and biochemical studies of the 5'-->3' exoribonuclease Xrn1. Chang JH, Xiang S, Xiang K, Manley JL, Tong L; Nat Struct Mol Biol. 2011;18:270-276. PMID:21297639