Involved in nuclear export of spliced and unspliced mRNA. Assembling component of the TREX complex which is thought to couple mRNA transcription, processing and nuclear export, and specifically associates with spliced mRNA and not with unspliced pre-mRNA. TREX is recruited to spliced mRNAs by a transcription-independent mechanism, binds to mRNA upstream of the exon-junction complex (EJC) and is recruited in a splicing- and cap-dependent manner to a region near the 5' end of the mRNA where it functions in mRNA export to the cytoplasm via the TAP/NFX1 pathway. May undergo several rounds of ATP hydrolysis during assembly of TREX to drive subsequent loading of components such as ALYREF/THOC and CHTOP onto mRNA. Also associates with pre-mRNA independent of ALYREF/THOC4 and the THO complex. Involved in the nuclear export of intronless mRNA; the ATP-bound form is proposed to recruit export adapter ALYREF/THOC4 to intronless mRNA; its ATPase activity is cooperatively stimulated by RNA and ALYREF/THOC4 and ATP hydrolysis is thought to trigger the dissociation from RNA to allow the association of ALYREF/THOC4 and the NXF1-NXT1 heterodimer. Involved in transcription elongation and genome stability. Splice factor that is required for the first ATP-dependent step in spliceosome assembly and for the interaction of U2 snRNP with the branchpoint. Has both RNA-stimulated ATP binding/hydrolysis activity and ATP-dependent RNA unwinding activity. Even with the stimulation of RNA, the ATPase activity is weak. Can only hydrolyze ATP but not other NTPs. The RNA stimulation of ATPase activity does not have a strong preference for the sequence and length of the RNA. However, ssRNA stimulates the ATPase activity much more strongly than dsRNA. Can unwind 5' or 3' overhangs or blunt end RNA duplexes in vitro. The ATPase and helicase activities are not influenced by U2AF2; the effect of ALYREF/THOC4 is reported conflictingly with [PubMed:23299939] reporting a stimulatory effect. (Microbial infection) The TREX complex is essential for the export of Kaposi's sarcoma-associated herpesvirus (KSHV) intronless mRNAs and infectious virus production. ATP + H2O = ADP + H(+) + phosphate Homodimer, and heterodimer with DDX39A (PubMed:11675789, PubMed:15833825, PubMed:14667819). Component of the transcription/export (TREX) complex at least composed of ALYREF/THOC4, DDX39B, SARNP/CIP29, CHTOP and the THO subcomplex; TREX seems to have dynamic structure involving ATP-dependent remodeling; in the complex bridges ALYREF/THOC4 and the THO complex, and, in a ATP-dependent manner, ALYREF/THOC4 and SARNP/CIP29 (PubMed:11675789, PubMed:15833825, PubMed:14667819, PubMed:15998806, PubMed:17984224, PubMed:20844015, PubMed:23299939). Component of the spliceosome. Interacts directly with U2AF2 (PubMed:9242493). Interacts with RBM8A, RNPS1 and SRRM1, FYTTD1/UIF, THOC1, MX1 and POLDIP3 (PubMed:12944400, PubMed:15870275, PubMed:19836239, PubMed:21859714, PubMed:22928037). Interacts with LUZP4 (PubMed:25662211). (Microbial infection) Interacts with human cytomegalovirus/HHV-5 protein UL69. Can translocate to the cytoplasm in the presence of MX1. TREX complex assembly seems to occur in regions surrounding nuclear speckles known as perispeckles. The helicase C-terminal domain mediates interaction with ALYREF/THOC4. Belongs to the DEAD box helicase family. DECD subfamily.