Role of the amino terminal RHAU-specific motif in the recognition and resolution of guanine quadruplex-RNA by the DEAH-box RNA helicase RHAU

Abstract

Under physiological conditions, guanine-rich sequences of DNA and RNA can adopt stable and atypical four-stranded helical structures called G-quadruplexes (G4). Such G4 structures have been shown to occur in vivo and to play a role in various processes such as transcription, translation and telomere maintenance. Owing to their high-thermodynamic stability, resolution of G4 structures in vivo requires specialized enzymes. RHAU is a human RNA helicase of the DEAH-box family that exhibits a unique ATP-dependent G4-resolvase activity with a high affinity and specificity for its substrate in vitro. How RHAU recognizes G4-RNAs has not yet been established. Here, we show that the amino-terminal region of RHAU is essential for RHAU to bind G4 structures and further identify within this region the evolutionary conserved RSM (RHAU-specific motif) domain as a major affinity and specificity determinant. G4-resolvase activity and strict RSM dependency are also observed with CG9323, the Drosophila orthologue of RHAU, in the amino terminal region of which the RSM is the only conserved motif. Thus, these results reveal a novel motif in RHAU protein that plays an important role in recognizing and resolving G4-RNA structures, properties unique to RHAU among many known RNA helicases.

Translational Repression of the Disintegrin and Metalloprotease ADAM10 by a Stable G-quadruplex Secondary Structure in Its 5′-Untranslated Region

“…Apart from FMRP and hnRNP A, there are several proteins described that are able to interact and modify G-quadruplex structures in DNA and RNA substrates. For instance, specific RNA and DNA helicases are able to unwind G-quadruplex structures (83)(84)(85)(86). Deficiencies of certain G-quadruplex resolving helicases result in abnormal mRNA deadenylation and decay and in perturbed telomere maintenance and cellular DNA replication, leading to cancer (87).…”

The 5′ Guanosine Tracts of Human Telomerase RNA Are Recognized by the G-Quadruplex Binding Domain of the RNA Helicase DHX36 and Function To Increase RNA Accumulation

“…Here, we demonstrate that guanosine tracts clustered near the hTR 5Ј end can be recognized by DHX36 and in particular by the DHX36 N-terminal domain specific for binding to Gquadruplex structures in vitro (25). Curiously, substitutions within the hTR guanosine tracts substantially reduce mature RNA accumulation.…”

“…The results above suggest that folding favors inclusion of the 5Ј leader 3-G tracts GGG(1-3), GGG (11)(12)(13), and GGG (15)(16)(17). In alternative folds, the fourth strand could be contributed by GG (8,9), GGG(21-23), or GGGG (25)(26)(27)(28). Formation of P1 would disfavor incorporation of the central P1 GGGG(25-28) tract more than the GGG(21-23) tract toward the base of the stem.…”

“…DHX36 (also known as RHAU and G4R1) is a DEXH box RNA helicase independently discovered as a mediator of AUrich element mRNA degradation and as a resolvase for Gquadruplex DNA in vitro (35,37). Subsequent studies expanded the function of DHX36 to include more global roles in regulating mRNA expression and to include resolvase activity on a model RNA as well as a DNA quadruplex of parallelstrand orientation (11,22,25). A previous mass spectrometry analysis of human telomerase holoenzyme affinity purified by tagged TERT (18) unreliably identified DHX36 and several other helicase domain proteins (unpublished results), with the inconclusive identifications based on only a single peptide sequence (in the case of DHX36) or peptide detection in parallel mock purifications from cells lacking tagged TERT (in the case of RuvBL1 and RuvBL2, the Unigene designations for proteins also known as TIP49 or pontin and TIP48 or reptin, respectively).…”

RNA helicases in infection and disease

“…The DExH box helicase DHX36 (RHAU, G4R1), a helicase mediating the degradation of mRNAs containing AU-rich elements, 173 recognizes these guanosine tracts in telomerase RNA. 174,175 DHX36 has been shown to resolve G-quadruplex DNA 176 and RNA 175 in vitro. While these findings link DHX36 to telomere maintenance, cancer and aging, its specific role is still unclear.…”