Practice question

Nuclear export of mature messenger ribonucleoproteins employs dedicated adaptors that recognize RNA processing marks rather than leucine-rich export signals. After splicing, exon junction complex and cap binding complex recruit TREX components including THO complex, UAP56 helicase and Aly/REF adaptor coating 5' region of transcript and providing platform for NXF1-NXT1 heterodimer, called TAP-p15 in metazoans, that binds via arginine-rich domains and directly engages FG nucleoporins through its NTF2-like and UBA domains for translocation. On cytoplasmic face, DDX19/Dbp5 helicase anchored by Nup214 interacts with Gle1 and inositol hexakisphosphate to stimulate ATP hydrolysis, displacing NXF1, Aly and other nuclear proteins, ensuring unidirectional release and immediate engagement with translation initiation factors. Ran-GTP essential for CRM1-mediated protein export is dispensable; leptomycin B that blocks CRM1 or Ran mutants leave bulk poly(A) export unaffected. While ATPase activity of Dbp5 is absolutely required for remodeling, generic ATPase not part of this pore-associated complex is unnecessary, so distinguishing specific Dbp5-dependent ATPase versus unrelated ATPase clarifies why mRNA export bypasses Ran system for continuous gene expression and surveillance.