NAP-2: histone chaperone function and phosphorylation state through the cell cycle.
We have recently cloned the human nucleosome assembly protein 2 (NAP-2). Here, we demonstrate that casein kinase 2 (CKII) from HeLa cell nuclear extracts interacts with immobilized NAP-II, and phosphorylates both NAP-2 and nucleosome assembly protein 1 (NAP-1) in vitro. Furthermore, NAP-1 and NAP-2 phosphorylation in crude HeLa cell extracts is abolished by heparin, a specific inhibitor of CKII. Addition of core histones can stimulate phosphorylation of NAP-1 and NAP-2 by CKII. NAP-2 is also a phosphoprotein in vivo. The protein is phosphorylated at the G0/G1 boundary but it is not phosphorylated in S-phase. Here, we show that NAP-2 is a histone chaperone throughout the cell cycle and that its cell-cycle distribution might be governed by its phosphorylation status. Phosphorylated NAP-2 remains in the cytoplasm in a complex with histones during the G0/G1 transition, whereas its dephosphorylation triggers its transport into the nucleus, at the G1/S-boundary, with the histone cargo, suggesting that binding to histones does not depend on phosphorylation status. Finally, indirect immunofluorescence shows that NAP-2 is present during metaphase of HeLa and COS cells, and its localization is distinct from metaphase chromosomes.
Rodriguez
P
P
McGill Cancer Center, Montreal, Quebec, Canada.
Pelletier
J
J
Price
G B
GB
Zannis-Hadjopoulos
M
M
D000818:Animals; D001692:Biological Transport; D047390:Casein Kinase II; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002846:Chromatography, Affinity; D002875:Chromosomes / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D016193:G1 Phase; D006367:HeLa Cells; D006493:Heparin / Q000494:pharmacology; D006657:Histones / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D008677:Metaphase; D018832:Molecular Chaperones / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D056490:Nucleosome Assembly Protein 1; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D016196:S Phase
D018797:Cell Cycle Proteins; D002457:Cell Extracts; D006657:Histones; D018832:Molecular Chaperones; C533557:NAP1L1 protein, human; C104356:NAP1L4 protein, human; D009687:Nuclear Proteins; D056490:Nucleosome Assembly Protein 1; D010750:Phosphoproteins; D011506:Proteins; D006493:Heparin; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases