title: Nuclear targeting determinants of the far upstream element binding protein, a c-myc transcription factor.
abstract: FUSE binding protein (FBP) binds in vivo and in vitro with the single-stranded far upstream element (FUSE) upstream of the c-myc gene. In addition to its transcriptional role, FBP and its closely related siblings FBP2 (KSRP) and FBP3 have been reported to bind RNA and participate in various steps of RNA processing, transport or catabolism. To perform these diverse functions, FBP must traffic to different nuclear sites. To identify determinants of nuclear localization, full-length FBP or fragments thereof were fused to green fluorescent protein. Fluorescent-FBP localized in the nucleus in three patterns, diffuse, dots and spots. Each pattern was conferred by a distinct nuclear localization signal (NLS): a classical bipartite NLS in the N-terminal and two non-canonical signals, an alpha-helix in the third KH-motif of the nucleic acid binding domain and a tyrosine-rich motif in the C-terminal transcription activation domain. Upon treatment with the transcription inhibitor actinomycin D, FBP completely re-localized into dots, but did not exit from the nucleus. This is in contrast to many general RNA-binding proteins, which shuttle from the nucleus upon treatment with actinomycin D. Furthermore, FBP co-localized with transcription sites and with the general transcription factor TFIIH, but not with the splicing factor SC-35. Taken together, these data reveal complex intranuclear trafficking of FBP and support a transcriptional role for this protein.
authors.affiliation: Laboratory of Pathology, DCS, NCI, Building 10, Room 2N105, Bethesda, MD 20892-1500, USA.
authors.forename: L
authors.initials: L
authors.lastname: He
authors.forename: A
authors.initials: A
authors.lastname: Weber
authors.forename: D
authors.initials: D
authors.lastname: Levens
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; C492258:FUBP1 protein, human; D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D016271:Proto-Oncogene Proteins c-myc; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D003609:Dactinomycin; D004265:DNA Helicases