Tap and NXT promote translation of unspliced mRNA.
Tap has been proposed to play a role in general mRNA export and also functions in expression of RNA with retained introns that contain the MPMV CTE (constitutive transport element). Tap forms a functional heterodimer with NXT/p15. We have previously demonstrated that unspliced intron-containing CTE RNA is efficiently exported to the cytoplasm in mammalian cells. Here we show that Tap and NXT proteins function together to enhance translation of proteins from the exported CTE RNA. Pulse chase experiments show that Tap/NXT significantly increases the rate of protein synthesis. Sucrose gradient analysis demonstrates that Tap and NXT efficiently shift the unspliced RNA into polyribosomal fractions. Furthermore, Tap, but not NXT is detected in polyribosomes. Taken together, our results indicate that Tap and NXT serve a role in translational regulation of RNA after export to the cytoplasm. They further suggest that Tap/NXT may play a role in remodeling of cytoplasmic RNP complexes, providing a link between export pathways and cytoplasmic fate.
Jin
Li
L
Myles H. Thaler Center for AIDS and Human Retrovirus Research, and Department of Microbiology, University of Virginia, Charlottesville, VA 22908, USA.
Guzik
Brian W
BW
Bor
Yeou-cherng
YC
Rekosh
David
D
Hammarskjöld
Marie-Louise
ML
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D021581:Active Transport, Cell Nucleus; D002352:Carrier Proteins / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D015685:Fusion Proteins, gag-pol / Q000235:genetics / Q000378:metabolism; D016655:HIV Core Protein p24 / Q000235:genetics / Q000378:metabolism; D015497:HIV-1 / Q000235:genetics; D006801:Humans; D008285:Major Histocompatibility Complex; D009154:Mutation; D029543:Nucleocytoplasmic Transport Proteins; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000235:genetics*; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D012190:Retroviridae / Q000502:physiology
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D015685:Fusion Proteins, gag-pol; D016655:HIV Core Protein p24; C498546:NXT1 protein, human; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; C073119:TAP1 protein, human