title: Nuclear localization conferred by the pocket domain of the retinoblastoma gene product.
abstract: The tumor suppressor Rb is a nuclear phosphoprotein that controls cell growth and differentiation by modulating the activity of certain transcription factors. Transport of Rb to the nucleus is affected by both a bipartite nuclear localization signal (NLS) in the C-terminus of the protein and a central domain, termed A/B or pocket, through which Rb interacts with transcription factors and viral oncoproteins. Mutations in either the A or B subdomains of the pocket render a NLS-deficient Rb completely cytoplasmic. Fusing the A/B domain of Rb to the Escherichia coli beta-galactosidase, to create betagal-A/B, confers nuclear localization upon this bacterial protein. Moreover, co-expression with the adenovirus oncoprotein, E1A, further augments nuclear localization of betagal-A/B. These findings provide direct evidence that the pocket domain of Rb is not only required but also sufficient to induce nuclear transport by a 'piggyback' mechanism. Thus, nuclear localization of Rb is dictated by two independent and autonomous domains: (i) the bipartite NLS and (ii) the pocket domain. We suggest that via these domains, Rb chaperons and co-compartmentalizes with its associated factors and preempts their activity prior to nuclear transport.
authors.affiliation: Departments of Medicine and Medical Biophysics, Oncology Research Laboratories, The Toronto Hospital, 67 College Street, Rm. 420, Toronto, Ont., Canada. eldad.zacksenhaus@utoronto.ca
authors.forename: E
authors.initials: E
authors.lastname: Zacksenhaus
authors.forename: Z
authors.initials: Z
authors.lastname: Jiang
authors.forename: Y J
authors.initials: YJ
authors.lastname: Hei
authors.forename: R A
authors.initials: RA
authors.lastname: Phillips
authors.forename: B L
authors.initials: BL
authors.lastname: Gallie
mesh_terms: D016475:3T3 Cells; D017500:Adenovirus E1A Proteins / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D051379:Mice; D010957:Plasmids; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured; D001616:beta-Galactosidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D017500:Adenovirus E1A Proteins; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D001616:beta-Galactosidase