Acts as an ATP-dependent RNA helicase, able to unwind both RNA-RNA and RNA-DNA duplexes. Possesses 5' single-stranded RNA overhang nuclease activity. Possesses ATPase activity on various RNA, but not DNA polynucleotides. May play a role in RNA clearance at DNA double-strand breaks (DSBs), thereby facilitating the template-guided repair of transcriptionally active regions of the genome. Together with RELA, acts as a coactivator to enhance NF-kappa-B-mediated transcriptional activation. Acts as a positive transcriptional regulator of cyclin CCND2 expression. Binds to the cyclin CCND2 promoter region. Associates with chromatin at the NF-kappa-B promoter region via association with RELA. Binds to poly(A) RNA. May be involved in 3'-end cleavage and polyadenylation of pre-mRNAs. Component of the tRNA-splicing ligase complex required to facilitate the enzymatic turnover of catalytic subunit RTCB: together with archease (ZBTB8OS), acts by facilitating the guanylylation of RTCB, a key intermediate step in tRNA ligation. Component of a multi-helicase-TICAM1 complex that acts as a cytoplasmic sensor of viral double-stranded RNA (dsRNA) and plays a role in the activation of a cascade of antiviral responses including the induction of pro-inflammatory cytokines via the adapter molecule TICAM1. Specifically binds (via helicase ATP-binding domain) on both short and long poly(I:C) dsRNA (By similarity). ATP + H2O = ADP + H(+) + phosphate Found in a multi-helicase-TICAM1 complex at least composed of DHX36, DDX1, DDX21 and TICAM1; this complex exists in resting cells with or without poly(I:C) RNA ligand stimulation (By similarity). Interacts with DHX36 (By similarity). Interacts (via B30.2/SPRY domain) with DDX21 (via N-terminus); this interaction serves as bridges to TICAM1 (By similarity). Interacts with FAM98A (via N- and C-terminus) (By similarity). Interacts with PHF5A (via C-terminus) (By similarity). Interacts with MBNL1 (By similarity). Interacts with CSTF2 (By similarity). Interacts with HNRNPK (By similarity). Interacts with ATM (By similarity). Interacts with RELA (via C-terminus) (By similarity). Component of the tRNA-splicing ligase complex (By similarity). Interacts with PQBP1 (By similarity). Interacts with ERCC6 (By similarity). Localized with MBNL1, TIAL1 and YBX1 in stress granules upon stress. Localized with CSTF2 in cleavage bodies. Forms large aggregates called DDX1 bodies. Relocalized into multiple foci (IR-induced foci or IRIF) after IR treatment, a process that depends on the presence of chromosomal DNA and/or RNA-DNA duplexes. Relocalized at sites of DNA double-strand breaks (DSBs) in an ATM-dependent manner after IR treatment. Colocalized with RELA in the nucleus upon TNF-alpha induction. Enters into the nucleus in case of active transcription while it accumulates in cytosol when transcription level is low. Colocalizes in the cytosol with DDX21, DHX36 and TICAM1. Colocalizes in the mitochondria with TICAM1 and poly(I:C) RNA ligand. The multi-helicase-TICAM1 complex may translocate to the mitochondria upon poly(I:C) stimulation (By similarity). The helicase domain is involved in the stimulation of RELA transcriptional activity. Phosphorylated by ATM kinase; phosphorylation is increased in response to ionizing radiation (IR). Belongs to the DEAD box helicase family. DDX1 subfamily.