title: Spatial regulation of the start repressor Whi5.
abstract: The Saccharomyces cerevisiae Start repressor Whi5, the functional analogue of mammalian pRB, shuttles between the nucleus and the cytoplasm throughout the cell cycle: enters into the nucleus at the end of mitosis and remains nuclear until Start. We studied the mechanisms involved in this spatial regulation. The nuclear import depends on the beta-karyopherins of the classical import pathway Kap95 and Cse1. Whi5 contains a monopartite and a bipartite classical NLS localized in its N-terminal region which are functionally redundant. A fragment of Whi5 containing these NLSs is able to constitutively accumulate a GFP(4) protein inside the nucleus throughout the cell cycle, which suggests that the Whi5 nuclear import is not cell cycle-regulated. The nuclear export of Whi5 is assisted by beta-karyopherin Msn5. A two-hybrid assay indicates a physical interaction between Whi5 and Msn5. We identified a fragment of Whi5 with export activity from amino acids 51 to 167. Interestingly, this region drives the export of a chimeric nuclear protein in a cell cycle-regulated pattern similarly to that observed for Whi5. Moreover, the nuclear export driven by Whi5(51-167) depends on the phosphorylation of specific Ser residues. Finally, we identified Cdc14 as the phosphatase required for the nuclear accumulation of Whi5.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Universitat de València, Burjassot (Valencia), Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Taberner
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Quilis
authors.forename: J Carlos
authors.initials: JC
authors.lastname: Igual
mesh_terms: D021581:Active Transport, Cell Nucleus; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D028884:Karyopherins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017027:Protein Tyrosine Phosphatases; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D028961:beta Karyopherins / Q000378:metabolism
chemical_list: C074860:CDC14 protein, S cerevisiae; D018797:Cell Cycle Proteins; D028884:Karyopherins; C401306:MSN5 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C508130:Whi5 protein, S cerevisiae; D028961:beta Karyopherins; D017027:Protein Tyrosine Phosphatases