The Nuclear Transport Machinery Recognizes Nucleoplasmin鈥揌istone Complexes

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• 作者：Igor Arregi ; Jorge Falces ; Sonia Ban虄uelos ; Marı ; &#769 ; a A. Urbaneja ; Stefka G. Taneva
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：August 23, 2011
• 年：2011
• 卷：50
• 期：33
• 页码：7104-7110
• 全文大小：329K
• 年卷期：v.50,no.33(August 23, 2011)
• ISSN：1520-4995

文摘

The nuclear transport of the chromatin remodeling protein nucleoplasmin and chromatin building histones is mediated by importins. Nucleoplasmin (NP) contains a classical bipartite nuclear localization signal (NLS) that is recognized by the importin 伪/尾 heterodimer, while histones present multiple NLS-like motifs that are recognized by importin 尾 family members for nuclear targeting. To explore the possibility of a cotransport of histones and their chaperone NP to the nucleus, we have analyzed the assembly of complexes of NP/histones with importins by means of fluorescence anisotropy, centrifugation in sucrose gradients, and isothermal titration calorimetry. Data show that importin 伪 螖IBB (a truncated form of importin 伪 lacking the autoinhibitory N-terminal domain) and histones (linker, H5, and nucleosomal core, H2AH2B) can simultaneously bind to NP. Analysis of the binding energetics reveals an enthalpy-driven formation of high affinity ternary, NP/螖伪/H5 and NP/螖伪/H2AH2B, complexes. We find that different amount of importin 伪 molecules can be loaded on NP/histone complexes dependent on the histone type, linker or core, and the amount of bound histones. We further demonstrate that NP/H5 complexes can also incorporate importin 伪/尾, thus forming quaternary NP/histones/伪/尾 complexes that might represent a putative coimport pathway for nuclear import of histones and their chaperone protein NP, enhancing the histone import efficiency.