title: Myb-binding protein 1a is a nucleocytoplasmic shuttling protein that utilizes CRM1-dependent and independent nuclear export pathways.
abstract: Myb-binding protein 1a (Mybbp1a) is a novel nuclear protein localized predominantly, but not exclusively, in nucleoli. Although initially isolated as a c-Myb interacting protein, Mybbp1a is expressed ubiquitously, associates with a number of different transcription factors, and may play a role in both RNA polymerase I- and II-mediated transcriptional regulation. However, its precise function remains unclear. In this study we show that Mybbp1a is a nucleocytoplasmic shuttling protein and investigate the mechanisms responsible for both nuclear import and export. The carboxyl terminus of Mybbp1a, which contains seven short basic amino acid repeat sequences, is responsible for both nuclear and nucleolar localization, and this activity can be transferred to a heterologous protein. Deletion mapping demonstrated that these repeat sequences appear to act incrementally, with successive deletions resulting in a corresponding increase in the proportion of protein localized in the cytoplasm. Glutathione S-transferase pulldown experiments showed that the nuclear receptor importin-alpha/beta mediates Mybbp1a nuclear import. Interspecies heterokaryons were used to demonstrate that Mybbp1a was capable of shuttling between the nucleus and the cytoplasm. Deletion analysis and in vivo export studies using a heterologous assay system identified several nuclear export sequences which facilitate Mybbp1a nuclear export of Mybbp1a by CRM1-dependent and -independent pathways.
authors.affiliation: Hanson Institute, Division of Human Immunology, Institute of Medical and Veterinary Science, Adelaide, South Australia 5000, Australia. rebecca.keough@adelaide.edu.au
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Keough
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Macmillan
authors.forename: Jodi K
authors.initials: JK
authors.lastname: Lutwyche
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Gardner
authors.forename: Fiona J
authors.initials: FJ
authors.lastname: Tavner
authors.forename: David A
authors.initials: DA
authors.lastname: Jans
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gonda
mesh_terms: D016475:3T3 Cells; D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002352:Carrier Proteins / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D003593:Cytoplasm / Q000378:metabolism* / Q000648:ultrastructure; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins; D017434:Protein Structure, Tertiary / Q000502:physiology; D016601:RNA-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D028901:alpha Karyopherins / Q000378:metabolism; D000097606:Exportin 1 Protein
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D028884:Karyopherins; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D016601:RNA-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D028901:alpha Karyopherins; D000097606:Exportin 1 Protein; C491719:MYBBP1A protein, human; C110421:Mybbp1a protein, mouse; C087978:karyopherin alpha 2