Nucleosome 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... 

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. 

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... 

The term M.c. was first coined by R. A.Laskey et al. [Nature 275 (1978) 416-420] to describe the action of nucleoplasmin, an acidic nuclear protein that mediates the in vitro assembly of nucleosomes from histones and DNA. In solutions of physiological ionic strength in vitro, DNA and histones interact to form a precipitate. If the histones are first mixed with a molar excess of nucleoplasmin, the positive charges of the histones are decreased by the nucleoplasmin subsequent addition of DNA results in the formation of soluble nucleosome cores and release of the nucleoplasmin. Further development of the M.c. concept was initiated by the work of R.J. Ellis on ribulose huphosphate carboxylase-oxygenase (rubisco). It has been suggested that prions may be rogue M.c. [R. J. Ellis S.M. van der Vies Arum. Rev. Biochem. 60 (1991) 321-347 R.J.Ellis etal. (eds.) Phil Trans. Roy. Soc. Land. B 338 (1993) 255-373 D.Wall etal. J.Biol. Chem. 270 (1995) 2139-2144 J.S.Weissman et al. Cell 84 (1996) 481 90 A. A. Antson et al Circular Assemblies Curr. Opin. Struct. Biol. 6 (1996) 142-150 P. A. Cole Chaperone-assisted protein expression Structure 4 (1996) 239-242]... 

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