Phosphorylation of p68 RNA helicase regulates RNA binding by the C-terminal domain of the protein

We previously reported ATPase, RNA unwinding, and RNA-binding activities of recombinant p68 RNA helicase that was expressed in Escherichia coli. Huang et al. [J. Biol. Chem. 277(15) (2002) 12810]. The recombinant protein bound both single-stranded (ss) and double-stranded (ds) RNAs. To further characterize the substrate RNA binding by p68 RNA helicase, we expressed and purified the recombinant N-terminal and C-terminal domains of the protein. RNA-binding property and protein phosphorylation of the recombinant domains of p68 were analyzed. Our data demonstrated that the C-terminal domain of p68 RNA helicase bound ssRNA. More interestingly, the C-terminal domain was a target of protein kinase C (PKC). Phosphorylation of the C-terminal domain of p68 abolished its RNA binding. Based on our observations, we propose that the C-terminal domain is an RNA substrate binding site for p68. The protein phosphorylation by PKC regulates the RNA binding of p68 RNA helicase, which consequently controls the enzymatic activities of the protein.