title: Characterization of the nuclear export signal of polypyrimidine tract-binding protein.
abstract: The polypyrimidine tract-binding protein (PTB) is a nuclear protein that regulates alternative splicing. In addition, it plays a role in the cytoplasm during infection by some viruses and functions as a positive effector of hepatitis B virus RNA export. Thus, it presumably contains a nuclear export signal (NES). Using a heterokaryon export assay in transfected cultured cells, we have shown that the N-terminal 25 amino acid residues of PTB function as an autonomous NES, with residues 11-16 being important for its activity. Unlike the heteronuclear ribonucleoprotein A1 NES, this NES is separable from the nuclear localization signal, which spans the entire N-terminal 60 residues of PTB. The PTB NES cannot be shown to bind to CAS or Crm1, cellular receptors known to export proteins from the nucleus, and it functions in the presence of leptomycin B, a specific inhibitor of Crm1-dependent export. PTB deleted of its NES, unlike wild type PTB, does not stimulate the export of hepatitis B virus RNA. Therefore, the PTB NES is a functionally important domain of this multifunctional protein that utilizes an unknown export receptor.
authors.affiliation: Pathology Service, Veterans Affairs Medical Center, San Francisco, California 94121, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.forename: T S Benedict
authors.initials: TS
authors.lastname: Yen
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D029563:Cellular Apoptosis Susceptibility Protein / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D015694:Gene Products, rev / Q000378:metabolism; D006515:Hepatitis B virus / Q000378:metabolism; D006801:Humans; D028884:Karyopherins / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D016133:Polymerase Chain Reaction; D038941:Polypyrimidine Tract-Binding Protein; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D012261:Ribonucleoproteins / Q000378:metabolism*; D014162:Transfection; D020798:Two-Hybrid System Techniques; D000097606:Exportin 1 Protein
chemical_list: D000903:Antibiotics, Antineoplastic; D029563:Cellular Apoptosis Susceptibility Protein; D018076:DNA, Complementary; D005231:Fatty Acids, Unsaturated; D015694:Gene Products, rev; D028884:Karyopherins; D038941:Polypyrimidine Tract-Binding Protein; D012313:RNA; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D012261:Ribonucleoproteins; D000097606:Exportin 1 Protein; C038753:leptomycin B