Probable ATP-binding RNA helicase (By similarity). Required for nonsense-mediated decay (NMD) degradation of mRNA transcripts containing premature stop codons (By similarity). Promotes the phosphorylation of UPF1 along with its interaction with key NMD pathway proteins UPF2 and EIF4A3 (By similarity). Negatively regulates the nucleotide binding ability and ATP hydrolysis of the RUVBL1-RUVBL2 complex via induction of N-terminus conformation changes of the RUVBL2 subunits (By similarity). ATP + H2O = ADP + H(+) + phosphate Forms a complex with RUVBL1 and RUVBL2 (By similarity). Part of a complex composed of SMG1, DHX34 and UPF1; within the complex DHX34 acts as a scaffolding protein to facilitate SMG1 phosphorylation of UPF1 (By similarity). Interacts with UPF1, MOV10, EIF4A3, XRN2, SMG6, SMG7, SMG9, UPF3A, UPF3B, CASC3/MLN51, XRN1, DIS3 and DCP1A; the interactions are RNA-independent (By similarity). Interacts with NCBP1/CPB80; the interaction is RNA-dependent (By similarity). Interacts (via C-terminus) with SMG1; the interaction is RNA-independent (By similarity). Belongs to the DEAD box helicase family. DEAH subfamily. Extended N-terminus.