Probable ATP-binding RNA helicase required for nonsense-mediated decay (NMD) degradation of mRNA transcripts containing premature stop codons (PubMed:25220460, PubMed:33205750). Promotes the phosphorylation of UPF1 along with its interaction with key NMD pathway proteins UPF2 and EIF4A3 (PubMed:25220460). Interaction with the RUVBL1-RUVBL2 complex results in loss of nucleotide binding ability and ATP hydrolysis of the complex (PubMed:33205750). 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 (PubMed:33205750). ATP + H2O = ADP + H(+) + phosphate Forms a complex with RUVBL1 and RUVBL2 (PubMed:33205750). 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 (PubMed:26841701). Interacts with UPF1, MOV10, EIF4A3, XRN2, SMG6, SMG7, SMG9, UPF3A, UPF3B, CASC3/MLN51, XRN1, DIS3 and DCP1A; the interactions are RNA-independent (PubMed:25220460). Interacts with NCBP1/CPB80; the interaction is RNA-dependent (PubMed:25220460). Interacts (via C-terminus) with SMG1; the interaction is RNA-independent (PubMed:25220460, PubMed:26841701). Expressed in whole blood, testis and spleen. Also expressed in the brain. Belongs to the DEAD box helicase family. DEAH subfamily. Aberrant splicing. Truncated N-terminus.