title: Delineation and modelling of a nucleolar retention signal in the coronavirus nucleocapsid protein.
abstract: Unlike nuclear localization signals, there is no obvious consensus sequence for the targeting of proteins to the nucleolus. The nucleolus is a dynamic subnuclear structure which is crucial to the normal operation of the eukaryotic cell. Studying nucleolar trafficking signals is problematic as many nucleolar retention signals (NoRSs) are part of classical nuclear localization signals (NLSs). In addition, there is no known consensus signal with which to inform a study. The avian infectious bronchitis virus (IBV), coronavirus nucleocapsid (N) protein, localizes to the cytoplasm and the nucleolus. Mutagenesis was used to delineate a novel eight amino acid motif that was necessary and sufficient for nucleolar retention of N protein and colocalize with nucleolin and fibrillarin. Additionally, a classical nuclear export signal (NES) functioned to direct N protein to the cytoplasm. Comparison of the coronavirus NoRSs with known cellular and other viral NoRSs revealed that these motifs have conserved arginine residues. Molecular modelling, using the solution structure of severe acute respiratory (SARS) coronavirus N-protein, revealed that this motif is available for interaction with cellular factors which may mediate nucleolar localization. We hypothesise that the N-protein uses these signals to traffic to and from the nucleolus and the cytoplasm.
authors.affiliation: Institute of Molecular and Cellular Biology, University of Leeds, Leeds, UK.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Reed
authors.forename: Brian K
authors.initials: BK
authors.lastname: Dove
authors.forename: Richard M
authors.initials: RM
authors.lastname: Jackson
authors.forename: Rebecca
authors.initials: R
authors.lastname: Collins
authors.forename: Gavin
authors.initials: G
authors.lastname: Brooks
authors.forename: Julian A
authors.initials: JA
authors.lastname: Hiscox
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002466:Cell Nucleolus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D019295:Computational Biology; D017124:Conserved Sequence; D000086462:Coronavirus Nucleocapsid Proteins; D001351:Infectious bronchitis virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007930:Leucine / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D019590:Nucleocapsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014709:Vero Cells
chemical_list: D000086462:Coronavirus Nucleocapsid Proteins; D019913:Nuclear Localization Signals; D019590:Nucleocapsid Proteins; D011994:Recombinant Proteins; D007930:Leucine