RNA-binding GUCT domain found in vertebrate RNA helicase II/Gualpha (RH-II/Gualpha), RNA helicase II/Gubeta (RH-II/Gubeta) and similar proteins
This subfamily corresponds to the Gu C-terminal (GUCT) domain of RH-II/Gualpha and RH-II/Gubeta, two paralogues found in vertebrates. RH-II/Gualpha, also termed nucleolar RNA helicase 2, or DEAD box protein 21, or nucleolar RNA helicase Gu, is a bifunctional enzyme that displays independent RNA-unwinding and RNA-folding activities. It unwinds double-stranded RNA in the 5' to 3' direction in the presence of Mg2+ through the domains in its N-terminal region. In contrast, it folds single-stranded RNA in an ATP-dependent manner and its C-terminal region is responsible for the Mg2+ independent RNA-foldase activity. RH-II/Gualpha consists of a DEAD box helicase domain (DEAD), a helicase conserved C-terminal domain (helicase_C), and a GUCT followed by three FRGQR repeats and one PRGQR sequence. The DEAD and helicase_C domains may play critical roles in the RNA-helicase activity of RH-II/Gualpha. The function of GUCT domain remains unclear. The C-terminal region responsible for the RNA-foldase activity does not overlap with the GUCT domain. RH-II/Gubeta, also termed ATP-dependent RNA helicase DDX50, or DEAD box protein 50, or nucleolar protein Gu2, shows significant sequence homology with RH-II/Gualpha. It contains a DEAD domain, a helicase_C domain, and a GUCT domain followed by an arginine-serine-rich sequence but not (F/P)RGQR repeats in RH-II/Gualpha. Both RH-II/Gualpha and RH-II/Gubeta localize to nucleoli, suggesting roles in ribosomal RNA production, but RH-II/Gubeta also localizes to nuclear speckles containing the splicing factor SC35, suggesting its possible involvement in pre-mRNA splicing. In contrast to RH-II/Gualpha, RH-II/Gubeta has RNA-unwinding activity, but no RNA-folding activity.
Jiyao W et al.(2023). "The conserved domain database in 2023.",