Exosome RNA helicase MTR4 is a conserved RNA helicase that functions together with the nuclear exosome and it is involved in processing of structured RNAs, including snRNAs and snoRNAs. It also plays a role in nuclear RNA surveillance pathways involving the so-called TRAMP complex [1,2]. It contains an arch domain, required for proper 5.8S rRNA processing, and appears to function independently of canonical helicase activity [3]. The arch domain comprises an helical stalk/elbow that flanks a KOW module which adopts a beta-barrel fold. This entry represents the helical stalk found at the N-terminal of KOW beta-barrel from MTR4 [1-3]. This entry also includes Ski2-like helicases which have an overall similar structure to MTR4 proteins. However, Ski2 from yeast does not have the KOW motif and the beta-barrel is tightly packed against the helical stalk [3].

1: Structural analysis reveals the characteristic features of Mtr4, a DExH helicase involved in nuclear RNA processing and surveillance. Weir JR, Bonneau F, Hentschel J, Conti E; Proc Natl Acad Sci U S A. 2010;107:12139-12144. PMID:20566885

2: Structure of the frequency-interacting RNA helicase: a protein interaction hub for the circadian clock. Conrad KS, Hurley JM, Widom J, Ringelberg CS, Loros JJ, Dunlap JC, Crane BR; EMBO J. 2016;35:1707-1719. PMID:27340124

3: The crystal structure of S. cerevisiae Ski2, a DExH helicase associated with the cytoplasmic functions of the exosome. Halbach F, Rode M, Conti E; RNA. 2012;18:124-134. PMID:22114319