Multifunctional ATP-dependent nucleic acid helicase that unwinds DNA and RNA in a 3' to 5' direction and that plays important roles in many processes, such as DNA replication, transcriptional activation, post-transcriptional RNA regulation, mRNA translation and RNA-mediated gene silencing. Requires a 3'-single-stranded tail as entry site for acid nuclei unwinding activities as well as the binding and hydrolyzing of any of the four ribo- or deoxyribo-nucleotide triphosphates (NTPs). Binds to DNA, RNA and small interfering siRNA. Plays a role in DNA replication at origins of replication and cell cycle progression. Plays a role as a transcriptional coactivator acting as a bridging factor between polymerase II holoenzyme and transcription factors or cofactors. Plays several roles in post-transcriptional regulation of gene expression. Promotes pre-mRNA alternative splicing activities of a subset of genes. As component of a large PER complex, is involved in the negative regulation of 3' transcriptional termination of circadian target genes. Component of the coding region determinant (CRD)-mediated complex that promotes cytoplasmic MYC mRNA stability. Plays a role in mRNA translation. Also plays a role in the RNA-induced silencing complex (RISC) loading complex (RLC) assembly, and hence functions in the RISC-mediated gene silencing process. Mediates the attachment of heterogeneous nuclear ribonucleoproteins (hnRNPs) to actin filaments in the nucleus. ATP + H2O = ADP + H(+) + phosphate Component of the coding region determinant (CRD)-mediated complex. Identified in mRNP granule complexes containing untranslated mRNAs. Associates with the RISC complex. Associates with the SMN complex. Associates with polysomes. Nucleoplasmic shuttling protein. Its nuclear import involves the nucleocytoplasmic transport receptor Importin alpha/Importin beta receptor pathway in a Ran-dependent manner. In interphase, localizes in nuclear stress granules and at perichromatin fibrils and in cytoplasmic ribonucleoprotein granules. Excluded from the mitotic nucleus as early as prophase and re-entered the nucleus at telophase. Localized in cytoplasmic mRNP granules containing untranslated mRNAs. DRBM domains cooperate for the binding to nucleic acid but not for unwinding helicase activity. The helicase-associated domain-2 (HA2) region is essential for the duplex RNA unwinding helicase activity. The minimal transactivation region (MTAD) mediates interaction with the RNA polymerase II holoenzyme and stimulates transcriptional activation. The oligonucleotide- or oligosaccharide-binding (OB-fold) and the repeated arginine and glycine-glycine (RGG) regions are dispensable for both RNA-binding and unwinding helicase activities. The RGG region contains both nuclear localization signal (NLS) and nuclear export signal (NES) and is necessary and sufficient for nucleocytoplasmic shuttling in a RNA-independent manner. Belongs to the DEAD box helicase family. DEAH subfamily.