General Structure/Important Features
These large protein complexes control selective transport of molecules between the nucleus and cytoplasm.
What are nuclear pore complexes (NPCs)?
This dense region of the nucleus is where ribosomal RNA is transcribed and ribosomal subunits begin to assemble.
What is the nucleolus?
This is the export receptor most commonly used by mRNA to exit the nucleus.
What is the Nxf1-Nxt1 export receptor?
This small RNA molecule is transcribed by RNA polymerase III and must move from the nucleus to the cytoplasm to help in translation.
What is tRNA?
After transcription, this complex binds to the 5′ cap of snRNA and marks it for export.
What is the cap-binding complex (CBC)?
These short, leucine-rich peptide motifs signal that a protein should be exported from the nucleus.
What are nuclear export signals (NES)?
These enzymes generate RNA transcripts in the nucleolus that combine with proteins to form ribonucleoproteins.
What are RNA polymerase I and RNA polymerase III?
This complex is recruited by a 5' cap.
What is the cap binding complex?
This receptor specifically binds to mature tRNAs in a RanGTP-dependent manner to export them from the nucleus.
What is Exportin-t?
This adaptor protein must first be phosphorylated by CK2 kinase to become active for export complex formation.
What is PHAX?
These FG-repeat proteins line the central channel of the NPC and enable selective passage of transport complexes.
What are barrier nucleoporins?
This adaptor protein binds the pre-60S ribosomal subunit and contains a leucine-rich nuclear export signal recognized by CRM1.
What is NMD3?
This subunit of TREX2 complex contains a trigger loop responsible for dissociating UAP56 from the complex.
What is GANP?
Before tRNAs can be exported, they must be properly processed, including the addition of this three-nucleotide tail at their 3′ end.
What is the CCA tail?
The complete snRNA export complex is composed of these key components (four).
What are snRNA + CBC + PHAX + CRM1–RanGTP?
This toxin blocks CRM1-dependent nuclear export, causing proteins with NES sequences to accumulate in the nucleus.
What is leptomycin B?
This protein is hypothesized to act as an adaptor for 40S export because it binds with CRM1 and contains a leucine-rich NES.
What is hRIO2?
These are the three main subunits of the TREX complex.
What are the THO subcomplex, UAP56, ALY?
In the cytoplasm, this protein stimulates the hydrolysis of RanGTP to RanGDP, causing export complexes to fall apart.
What is Ran-GAP?
What two proteins catalyze the hydrolysis of GTP to GDP, converting RanGTP to RanGDP after the snRNA export complex has reached the cytoplasm, and what does this cause?
What are RanGAP and RanBP1, and they cause the disassembly of the snRNA export complex by converting RanGTP to RanGDP, releasing snRNA and dissociating CRM1, PHAX, and CBC in the cytoplasm?
This Ran-dependent export receptor, also known as Exportin 1, binds NES-containing cargo for transport through the NPC.
What is CRM1?
In 1989, Khanna Gupta and Ware showed that ribosomal subunits can pass through the nuclear pore complex using this experimental approach.
What is injecting radiolabeled ribosomes into Xenopus (frog) oocyte nuclei and tracking their movement?
This is one of the cytoplasmic filament nucleoporins that activates DDX19 ATPase via docking and allows the release of the export receptors and other RNA-binding proteins from the mRNP.
What is Gle1 / Nup42 / Nup214?
If Ran cannot hydrolyze GTP in the cytoplasm, this step of tRNA nuclear export would fail to occur.
What is the release of tRNA from Exportin-t (the export complex wouldn’t dissociate)?
In Ohno et al. (2000), researchers did this to isolate and confirm PHAX as the missing adaptor needed to link the snRNA-CBC complex to CRM1-RanGTP.
What is fractionating HeLa nuclear extracts and testing each fraction’s ability to restore export complex formation using a gel mobility shift assay, then identifying the active fraction by mass spectrometry?