Nucleoplasmin

The assembly of nucleosomes is mediated by one of several chromatin assembly factors facilitated by histone chaperones, proteins such as the anionic nuclear protein nucleoplasmin. As the nucleosome is assembled, histones are released from the histone chaperones. Nucleosomes appear to exhibit preference for certain regions on specific DNA molecules, but the basis for this nonrandom distribution, termed phasing, is not completely... 

Bipartite basic NLS Nucleoplasmin type two clusters containing basic residues, separated by spacer of about 10 aa Importin /3/importin a family... 

Robbins, J., Dilworth, S., Laskey, R., and Dingwall, C. (1991). Two interdependent basic domains in nucleoplasmin nuclear targeting sequence identification of a class of bipartite nuclear targeting sequences. Cell 64, 615-623. 

The term "molecular chaperone" is not novel and was first introduced (7) to describe the transient association of nucleoplasmin with the histones during the formation of nucleosomes. Subsequently, a similar transient association was found in the chloroplast of higher plants between nascent Large subunits (LSU) of die enzyme Ribulose bisphosphate carboxylase (Rubisco) and a SdOkDa protein complex composed of 12-14 60kDa subunits (2). The nascent chloroplast-synthesized LSU was found to bind this complex in a non-covalent manner and in sub-stoichiometric amounts. 

Chen, H., Li, B., and Workman, J.L. (1994). A histone-binding protein, nucleoplasmin, stimulates transcription factor binding to nucleosomes and factor-induced nucleosome disassembly. EMBO J. 75 380-390. 

Leno, G.H., Mills, A.D., Philpott, A., and Laskey, R.A. (1996). Hyperphosphorylation of nucleoplasmin facilitates Xenopus sperm decondensation at fertilization. J. Biol. Chem. 277 7253-7256. 

Ohsumi, K. and Katagiri, C. (1991). Characterization of the ooplasmic factor inducing decondensation of and protamine removal from toad sperm nuclei Involvement of nucleoplasmin. Dev. Biol. 748 295-305. 

Indeed, using extracts from amphibian eggs, it has been shown that the acidic protein nucleoplasmin, previously shown to function as a nucleosome assembly factor (for review, see Laskey and Leno, 1990), also plays a key role in the decondensation and remodeling of sperm chromatin at fertilization (Philpott et... 

Fig. 2 Two-dimensional PAGE analysis of sperm-associated proteins on condensed chromatin and following chromatin decondensation in egg extract and purified nucleoplasmin. Sperm nuclei were incubated in either (A) buffer, (B) Xenopus egg HSS, or (C) purified egg nucleoplasmin for 10 min. The nuclei were then pelleted, washed, and the chromatin-associated proteins were extracted with acid and analyzed in the first dimension by Triton-acid-urea (TAU)-PACE (left to right) and in the second dimension by SDS-PAGE (top to bottom). The positions of the core histones are indicated as H2A, H2B. H3. and H4 and the sperm-specific basic proteins as X and Y. The arrowheads and arrow indicate the positions of the cleavage-stage linker histone. B4, and Xenopus HMG-2, respectively (Dimitrov et at., 1994). [Reproduced from Philpott and Leno (1992) Copyright Cell Press.]...

Ito, T., Tyler, J. K., Bulger, M., Kobayashi, R., and Kadanaga, J. (1996). ATP-facilitated chromatin assembly with a nucleoplasmin-like protein from Drosophila melanogaster. J. Biol. Chem. 271, 25041-25048. 

Itoh, T., Ohsumi, K., and Katagiri, C. (1993). Remodeling of human sperm chromatin mediated by nucleoplasmin from amphibian eggs. Dev., Growth Differ. 35, 59-66. 

Leno, G. H., Philpott, A., and Laskey, R. A. (1993). Chromatin remodeling by nucleoplasmin. In John Innes Symposium The Chromosome (J. S. Heslop-Harrison and R. B. Flavell, eds.), pp. 135-147. Bios Scientific Publishers, Oxford. 

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