RNA-UNWINDING AND RNA-FOLDING ACTIVITIES OF RNA HELICASE-II GU - 2 ACTIVITIES IN SEPARATE DOMAINS OF THE SAME PROTEIN

The human RNA helicase II/Gu protein (RH-II/Gu) is a member of the D-E -A-D box protein family. It is a unique enzyme, which possesses an ATP -dependent RNA-unwinding activity and has an RNA-folding activity that introduces an intramolecular secondary structure in single-stranded R NA. This report shows that these two enzymatic activities are distinct . ATP[S], GTP and low concentrations of ATP enhance the RNA-folding ac tivity of RH-II/Gu but not the RNA-helicase activity. High concentrati ons of ATP are required for the helicase activity but are inhibitory t o the RNA-folding activity. Mg2+ is required for the helicase activity but not for the RNA-folding reaction. affinity-purified anti-(RH-II/G u) polyclonal Ig inhibit the RNA-unwinding activity but not the foldin g activity, Mutations of the DEVD sequence, which corresponds to the D EAD box, and the SAT motif enhanced RNA-folding activity of RU-II/Cu b ut completely inhibited the RNA-helicase activity. A mutant that lacks the COOH-terminal 76 amino acid residues, including the four FRGQR re peats, had unwinding activity but did not catalyze the folding of a si ngle-stranded RNA. The two enzymatic activities of RH-II/Gu reside in distinct domains. Amino acids 1-650 are active in the RNA-unwinding re action but lack RNA-folding activity. Amino acids 646-801 fold single- stranded RNA but lack helicase activity. This report shows distinct RN A-unwinding and RNA-folding activities residing in separate domains wi thin the same protein.