Involved in the alternative regulation of pre-mRNA splicing; its RNA helicase activity is necessary for increasing tau exon 10 inclusion and occurs in a RBM4-dependent manner. Binds to the tau pre-mRNA in the stem-loop region downstream of exon 10. The rate of ATP hydrolysis is highly stimulated by single-stranded RNA. Involved in transcriptional regulation; the function is independent of the RNA helicase activity. Transcriptional coactivator for androgen receptor AR but probably not ESR1. Synergizes with DDX17 and SRA1 RNA to activate MYOD1 transcriptional activity and involved in skeletal muscle differentiation. Transcriptional coactivator for p53/TP53 and involved in p53/TP53 transcriptional response to DNA damage and p53/TP53-dependent apoptosis. Transcriptional coactivator for RUNX2 and involved in regulation of osteoblast differentiation. Acts as transcriptional repressor in a promoter-specific manner; the function probably involves association with histone deacetylases, such as HDAC1. As component of a large PER complex is involved in the inhibition of 3' transcriptional termination of circadian target genes such as PER1 and NR1D1 and the control of the circadian rhythms. ATP + H2O = ADP + H(+) + phosphate Identified in the spliceosome C complex (PubMed:11991638). Component of a ribonucleoprotein complex containing mRNAs and RNA-binding proteins including DDX5, HNRNPH2 and SRSF1 as well as splicing regulator ARVCF (PubMed:24644279). Interacts with RBM4; the interaction occurs in an RNA-independent manner. Interacts with AGO1 and AGO2. Interacts with ESR1, AR, EP300, CREBBP, POLR2A, TP53, RUNX2 and HDAC1. Self-associates. Interacts with DDX17. Interacts with BRDT. The large PER complex involved in the repression of transcriptional termination is composed of at least PER2, CDK9, DDX5, DHX9, NCBP1 and POLR2A (active). Interacts with DHX36; this interaction occurs in a RNA-dependent manner (PubMed:18279852). Interacts with NUPR1 (By similarity). Interacts with ERCC6 (PubMed:26030138). Interacts with DDX3X in the cytoplasm; this interaction may be more efficient when both proteins are unphosphorylated (PubMed:22034099). During the G0 phase, predominantly located in the nucleus. Cytoplasmic levels increase during the G1/S phase. During the M phase, located at the vicinity of the condensed chromosomes. At G1, localizes in the cytoplasm. Arg-502 is dimethylated, probably to asymmetric dimethylarginine. Sumoylated; sumoylation, promoted by PIAS1, promotes interaction with HDAC1 and transcriptional repression activity. Sumoylation also significantly increases stability, and reduces polyubiquitination. Polyubiquitinated, leading to proteasomal degradation. Weakly phosphorylated in the G1/S phase of the cell cycle and much more at G2/M, especially at Thr and Tyr residues. Belongs to the DEAD box helicase family. DDX5/DBP2 subfamily. DDX5 was reported to be a transcriptional coactivator of ESR1. However, this study has been retracted due to concerns of image manipulation.