Phosphorylation of both nucleoplasmin domains is required for activation of its chromatin decondensation activity.
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.
Bañuelos
Sonia
S
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.
Omaetxebarria
Miren J
MJ
Ramos
Isbaal
I
Larsen
Martin R
MR
Arregi
Igor
I
Jensen
Ole N
ON
Arizmendi
Jesus M
JM
Prado
Adelina
A
Muga
Arturo
A
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
D000596:Amino Acids; D002843:Chromatin; D006657:Histones; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D056489:Nucleoplasmins; D010455:Peptides; D010750:Phosphoproteins