Stimulator of protein export for NES-containing proteins. Also plays a role in the nuclear export of U1 snRNA, tRNA, and mRNA. The NXF1-NXT1 heterodimer is involved in the export of HSP70 mRNA in conjunction with ALYREF/THOC4 and THOC5 (By similarity). Heterodimer with NXF1. Forms a complex with RANGAP1, RANBP2/NUP358 and NXF1. Interacts (via NTF2 domain) with NXF1. Stabilizes the NTF2 domain of NXF1 by heterodimerization. The formation of NXF1-NXT1 heterodimers is required for the NXF1-mediated nuclear mRNA export. Preferentially binds Ran-GTP. Associates with NXF2, NXF3 and NXF5. Does not bind nucleoporins (NPC) directly, its association to NPC is mediated by NXF1. Shuttles between the nucleus and the cytoplasm.