title: Phosphorylation of both nucleoplasmin domains is required for activation of its chromatin decondensation activity.
abstract: Nucleoplasmin (NP) is a histone chaperone involved in nucleosome assembly, chromatin decondensation at fertilization, and apoptosis. To carry out these activities NP has to interact with different types of histones, an interaction that is regulated by phosphorylation. Here we have identified a number of phosphorylated residues by mass spectrometry and generated mutants in which these amino acids are replaced by Asp to mimic the effect of phosphorylation. Our results show that, among the eight phosphoryl groups experimentally detected, four are located at the flexible N terminus, and the rest are found at the tail domain, flanking the nuclear localization signal. Phosphorylation-mimicking mutations render a recombinant protein as active in chromatin decondensation as hyperphosphorylated NP isolated from Xenopus laevis eggs. Comparison of mutants in which the core and tail domains of the protein were independently or simultaneously "activated" indicates that activation or phosphorylation of both protein domains is required for NP to efficiently extract linker-type histones from chromatin.
authors.affiliation: Unidad de Biofísica (Consejo Superior de Investigaciones Científicas-Universidad del Pais Vasco/Euskal Herriko Unibertsitatea), Facultad de Ciencia y Tecnología, Universidad del País Vasco, P. O. Box 644, 48080 Bilbao, Spain.
authors.forename: Sonia
authors.initials: S
authors.lastname: Bañuelos
authors.forename: Miren J
authors.initials: MJ
authors.lastname: Omaetxebarria
authors.forename: Isbaal
authors.initials: I
authors.lastname: Ramos
authors.forename: Martin R
authors.initials: MR
authors.lastname: Larsen
authors.forename: Igor
authors.initials: I
authors.lastname: Arregi
authors.forename: Ole N
authors.initials: ON
authors.lastname: Jensen
authors.forename: Jesus M
authors.initials: JM
authors.lastname: Arizmendi
authors.forename: Adelina
authors.initials: A
authors.lastname: Prado
authors.forename: Arturo
authors.initials: A
authors.lastname: Muga
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism; D006657:Histones / Q000737:chemistry; D013058:Mass Spectrometry; D018832:Molecular Chaperones / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry*; D056489:Nucleoplasmins; D010455:Peptides / Q000737:chemistry; D010750:Phosphoproteins / Q000737:chemistry*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002843:Chromatin; D006657:Histones; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D056489:Nucleoplasmins; D010455:Peptides; D010750:Phosphoproteins