DDX39B Protein, Human (GST)

The DDX39B protein is intricately involved in the nuclear export of both spliced and unspliced mRNA. As a crucial component of the TREX complex, it plays a pivotal role in coupling mRNA transcription, processing, and nuclear export, specifically associating with spliced mRNA rather than unspliced pre-mRNA. TREX is recruited to spliced mRNAs through a transcription-independent mechanism, binding to mRNA upstream of the exon-junction complex (EJC) and participating in mRNA export to the cytoplasm through the TAP/NFX1 pathway. During the assembly of TREX, DDX39B may undergo multiple rounds of ATP hydrolysis, driving the subsequent loading of components such as ALYREF/THOC and CHTOP onto mRNA. Additionally, DDX39B is implicated in the nuclear export of intronless mRNA, where its ATP-bound form recruits the export adapter ALYREF/THOC4 to intronless mRNA, with ATP hydrolysis triggering dissociation from RNA, allowing the association of ALYREF/THOC4 and the NXF1-NXT1 heterodimer. Beyond its role in mRNA export, DDX39B is involved in transcription elongation and contributes to genome stability. Functioning as a splice factor, it is essential for the initial ATP-dependent step in spliceosome assembly and the interaction of U2 snRNP with the branchpoint. DDX39B exhibits RNA-stimulated ATP binding/hydrolysis activity and ATP-dependent RNA unwinding activity, with a preference for ssRNA over dsRNA. Notably, its ATPase and helicase activities remain largely unaffected by U2AF2, while the impact of ALYREF/THOC4 stimulation is reported with conflicting findings.