Interaction of Nucleoplasmin with Core Histones

Nucleoplasmin is one of the most abundant proteins in Xenopus laevis oocytes, and it has been involved in the chromatin remodeling that takes place immediately after fertilization. This molecule has been shown to be responsible for the removal of the sperm-specific proteins and deposition of somatic histones onto the male pronuclear chromatin. To better understand the latter process, we have used sedimentation velocity, sedimentation equilibrium, and sucrose gradient fractionation analysis to show that the pentameric form of nucleoplasmin binds to a histone octamer equivalent consisting of equal amounts of the four core histones, H2A, H2B, H3, and H4, without any noticeable preference for any of these proteins. Removal of the histone N-terminal “tail” domains or the major C-terminal polyglutamic tracts of nucleoplasmin did not alter these binding properties. These results indicate that interactions other than those electrostatic in nature (likely hydrophobic) also play a critical role in the formation of the complex between the negatively charged nucleoplasmin and positively charged histones. Although the association of histones with nucleoplasmin may involve some ionic interactions, the interaction process is not electrostatically driven. Nucleoplasmin is one of the most abundant proteins in Xenopus laevis oocytes, and it has been involved in the chromatin remodeling that takes place immediately after fertilization. This molecule has been shown to be responsible for the removal of the sperm-specific proteins and deposition of somatic histones onto the male pronuclear chromatin. To better understand the latter process, we have used sedimentation velocity, sedimentation equilibrium, and sucrose gradient fractionation analysis to show that the pentameric form of nucleoplasmin binds to a histone octamer equivalent consisting of equal amounts of the four core histones, H2A, H2B, H3, and H4, without any noticeable preference for any of these proteins. Removal of the histone N-terminal “tail” domains or the major C-terminal polyglutamic tracts of nucleoplasmin did not alter these binding properties. These results indicate that interactions other than those electrostatic in nature (likely hydrophobic) also play a critical role in the formation of the complex between the negatively charged nucleoplasmin and positively charged histones. Although the association of histones with nucleoplasmin may involve some ionic interactions, the interaction process is not electrostatically driven. Under physiological conditions core histones interact with each other to form a heterotypic histone octamer consisting of a histone H3-H4 tetramer and two histone H2A-H2B dimers (1van Holde K.E. Chromatin. Springer-Verlag, New York1988Google Scholar, 2Luger K. Mader A.W. Richmond R.K. Sargent D.F. Richmond T.J. Nature. 1997; 389 (226): 251Crossref PubMed Scopus (6830) Google Scholar), which constitute the protein core of the basic chromatin subunit, the nucleosome core particle (1van Holde K.E. Chromatin. Springer-Verlag, New York1988Google Scholar, 2Luger K. Mader A.W. Richmond R.K. Sargent D.F. Richmond T.J. Nature. 1997; 389 (226): 251Crossref PubMed Scopus (6830) Google Scholar). In solution and in the absence of DNA the histone octamer exists in an equilibrium between its constitutive H2A-H2B dimers and the H3-H4 tetramer, which has been extensively characterized (3Eickbush T.H. Moudrianakis E.N. Biochemistry. 1978; 17: 4955-4964Crossref PubMed Scopus (273) Google Scholar). In contrast, nucleoplasmin is a pentameric acidic protein (4Earnshaw W.C. Honda B.M. Laskey R.A. Thomas J.O. Cell. 1980; 21: 373-383Abstract Full Text PDF PubMed Scopus (166) Google Scholar, 5Dingwall C. Sharnick S.V. Laskey R.A. Cell. 1982; 30: 449-458Abstract Full Text PDF PubMed Scopus (336) Google Scholar, 6Dutta S. Akey I.V. Dingwall C. Hartman K.L. Laue T. Nolte R.T. Head J.F. Akey C.W. Mol. Cell. 2001; 8: 841-853Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 7Akey C.W. Luger K. Curr. Opin. Struct. Biol. 2003; 13: 6-14Crossref PubMed Scopus (162) Google Scholar, 8Namboodiri V.M.H. Dutta S. Akey I.V. Head J.F. Structure. 2003; 11: 175-186Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar) that has been involved in the remodeling of the male pronuclear chromatin after fertilization of the oocyte in vertebrates (9Philpott A. Leno G.H. Cell. 1992; 69: 759-767Abstract Full Text PDF PubMed Scopus (195) Google Scholar, 10Laskey R.A. Mills A.D. Philpott A. Leno G.H. Dilworth S.M. Dingwall C. Philos. Trans. R. Soc. Lond.-Biol. Sci. 1993; 339: 263-269Crossref PubMed Scopus (58) Google Scholar, 11Katagiri C. Ohsumi K. Int. J. Dev. Biol. 1994; 38: 209-216PubMed Google Scholar, 12Ohsumi K. Katagiri C. Dev. Biol. 1991; 148: 295-305Crossref PubMed Scopus (71) Google Scholar, 13Saperas N. Chiva M. Aligué R. Itoh T. Katagiri C. Subirana J.A. Ausió J. Arch. Biochem. Biophys. 1999; 361: 135-141Crossref PubMed Scopus (13) Google Scholar) and invertebrate organisms (14Rice P. Garduno R. Itoh T. Katagiri C. Ausió J. Biochemistry. 1995; 34: 7563-7568Crossref PubMed Scopus (31) Google Scholar). Nucleoplasmin can bind and remove the protamine complement of the male pronucleus and can also bind to maternal histones mediating the replacement of the former by the latter. The way in which all this occurs at the molecular level has proven to be more complicated than originally envisaged. For instance, the early hypothetical model in which the highly positively charged protamines electrostatically interact with the negatively charged nucleoplasmin (10Laskey R.A. Mills A.D. Philpott A. Leno G.H. Dilworth S.M. Dingwall C. Philos. Trans. R. Soc. Lond.-Biol. Sci. 1993; 339: 263-269Crossref PubMed Scopus (58) Google Scholar) has been shown to be an oversimplification of the interactions involved (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar), and a detailed physical characterization of the interaction of nucleoplasmin with histones is lacking. Thus the precise molecular mechanisms by which early developmental chromatin remodeling takes place are still poorly understood. Recombinant Proteins and Histones—Recombinant nucleoplasmin was obtained by expression of plasmid pET20b containing the Xenopus laevis nucleoplasmin cDNA corresponding to the cDNA sequenced by Bürglin (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar). Recombinant nucleoplasmin lacking the C-terminal main polyglutamic tract of the molecule (r-NP121) was prepared as described (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar). Native and trypsinized histone octamers were obtained from chicken erythrocyte nucleosomes with or without treatment with immobilized trypsin (16Ausió J. Dong F. van Holde K.E. J. Mol. Biol. 1989; 206: 451-463Crossref PubMed Scopus (282) Google Scholar) upon elution from a hydroxylapatite column using a 2 m NaCl, 100 mm potassium phosphate (pH 6.8) buffer (17Wang X. Moore S.C. Laszckzak M. Ausió J. J. Biol. Chem. 2000; 275: 35013-35020Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar). Determination of Protein Concentrations—The concentration of nucleoplasmin was determined from the absorbance at 276 nm (13Saperas N. Chiva M. Aligué R. Itoh T. Katagiri C. Subirana J.A. Ausió J. Arch. Biochem. Biophys. 1999; 361: 135-141Crossref PubMed Scopus (13) Google Scholar). The concentration of histone octamers was determined using an absorption coefficient at 230 nm of 4.2 cm2 mg–1 (18Stein A. J. Mol. Biol. 1979; 130: 103-134Crossref PubMed Scopus (125) Google Scholar). The extinction coefficient of the trypsinized histones was calculated from their respective amino acid sequences according to Gill and von Hippel (19Gill S.C. von Hippel P.H. Anal. Biochem. 1989; 182: 319-326Crossref PubMed Scopus (5034) Google Scholar) as described by Luger et al. (20Luger K. Rechsteiner T.J. Richmond T.J. Methods Mol. Biol. 1999; 119: 1-16PubMed Google Scholar). Titration of Nucleoplasmin with Histone Octamers—Native or trypsinized histone octamers at a concentration of ∼3–4 mg/ml in 2 m NaCl, 100 mm potassium phosphate (pH 6.8) buffer were rapidly mixed with a nucleoplasmin solution prepared in 2 mm MgCl2, 10mm Tris-HCl (pH 7.5) buffer. The mixture was carried out in such a way that the final concentration of nucleoplasmin in all the samples (∼0.1–0.12 mg/ml) and the final buffer composition (0.24 m NaCl, 12 mm potassium phosphate, 8.8 mm Tris-HCl, 1.8 mm MgCl2 (pH 7.5)) were kept the same in all the samples. Analytical Ultracentrifuge Analysis—Sedimentation velocity and sedimentation equilibrium analyses were carried out with a Beckman XL-A analytical ultracentrifuge (Beckman-Coulter, Inc., Fullerton, CA) using An-55 AL 9 aluminum and An-60 Ti (titanium) rotors, respectively. The samples were loaded on Kel-F 12-mm double sector cells. Experiments were carried out at 20 °C at different speeds as indicated in the figure legends. Sedimentation velocity scans were analyzed using XL-A Ultra Scan version 4.1 sedimentation data analysis software (Borries Demeler, Missoula, MT), which employs a published method of boundary analysis (21van Holde K.E. Weischet W.O. Biopolymers. 1978; 17: 1387-1403Crossref Scopus (318) Google Scholar). Sedimentation equilibrium scans were analyzed using the XL-A data software analysis. The molecular weight average was calculated from the best fitting slope of ln of absorbance at 230 nm versus the square of the radial distance. The partial specific volume of nucleoplasmin was calculated from its amino acid composition following the method of Cohn and Edsall (22Cohn E.J. Edsall J.T. Proteins, Amino Acids and Peptides as Ions and Dipolar Ions. Reinhold Publishing Corporation, New York1943Crossref Google Scholar) using the amino acid partial specific volumes from Perkins (23Perkins S.J. Eur. J. Biochem. 1986; 157: 169-180Crossref PubMed Scopus (540) Google Scholar). The value calculated in this way was v̄ = 0.734 cm3/g. A value of v̄ = 0.753 cm3/g was used for the histone octamer (3Eickbush T.H. Moudrianakis E.N. Biochemistry. 1978; 17: 4955-4964Crossref PubMed Scopus (273) Google Scholar). Sucrose Gradients—Sucrose gradients (5–20% sucrose) were prepared in 240 mm NaCl, 12 mm potassium phosphate, 1.8 mm MgCl2, 8.8 mm Tris-HCl (pH 7.5) buffer. Native or trypsinized histones at ∼2.5 mg/ml in 2 m NaCl, 100 mm potassium phosphate buffer (pH 6.8) were rapidly mixed with a 0.25 mg/ml nucleoplasmin solution in 2 mm MgCl2, 10 mm Tris-HCl (pH 7.5) buffer at different stoichiometric ratios and were immediately loaded on the sucrose gradients. The gradients were run for 21.5 h at 103,800 × g at 4 °C. Electrophoretic analysis of the proteins was carried out by SDS-PAGE (15% polyacrylamide) (24Laemmli U.K. Nature. 1970; 227: 680-685Crossref PubMed Scopus (206514) Google Scholar). The Pentameric Form of Nucleoplasmin Binds Core Histones in an Amount Equivalent to One Histone Octamer—Native core histones (see Fig. 1a , lane 1) at elevated ionic strength (≥2 m NaCl) and at high concentrations of protein exist as a globular histone octamer (25Arents G. Burlingame R.W. Wang B.C. Love W.E. Moudrianakis E.N. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 10148-10152Crossref PubMed Scopus (605) Google Scholar) held together by specific interactions between the “histone fold” (2Luger K. Mader A.W. Richmond R.K. Sargent D.F. Richmond T.J. Nature. 1997; 389 (226): 251Crossref PubMed Scopus (6830) Google Scholar, 26Arents G. Moudrianakis E.N. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 11170-11174Crossref PubMed Scopus (287) Google Scholar) domains of these proteins. Under these high ionic strength conditions the histone octamer (M r = 108,000) sediments with an s 20,w = 3.9 ± 0.1 S (27Weintraub H. Palter K. Van Lente F. Cell. 1975; 6: 85-110Abstract Full Text PDF PubMed Scopus (243) Google Scholar, 28Thomas J.O. Butler P.J. J. Mol. Biol. 1977; 116: 769-781Crossref PubMed Scopus (88) Google Scholar, 29Chung S.Y. Hill W.E. Doty P. Proc. Natl. Acad. Sci. U. S. A. 1978; 75: 1680-1684Crossref PubMed Scopus (44) Google Scholar, 30Philip M. Jamaluddin M. Sastry R.V. Chandra H.S. Proc. Natl. Acad. Sci. U. S. A. 1979; 76: 5178-5182Crossref PubMed Scopus (17) Google Scholar). At lower ionic strengths, near physiological conditions the octamer is fully dissociated into a histone H3-H4 tetramer (M r = 53,200) and two histone H2A-H2B dimers (M r = 27,700 × 2). This heterogeneous mixture exhibits a sedimentation coefficient of 1.6–2.0 S for native histones and 2.0–2.4 S in the case of the trypsinized histones (see Fig. 1, a and b). The slight increase in s 20,w despite the decrease in mass observed in the latter case emphasizes the extended conformation of the histone domains (tails) removed by trypsin. It is not possible with the current technology to accurately define the individual sedimentation coefficients of the H3-H4 tetramer and the H2AH2B dimer from a mixture of both complexes. In contrast, nucleoplasmin forms under physiological conditions a stable pentamer (M r = 110,000), which has a sedimentation coefficient of 6.5 ± 0.1 S (see Fig. 1c) (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar). Although the preparation of recombinant nucleoplasmin used by us is very pure as judged by SDS-PAGE (see Fig. 1a , lane 3), it contains ∼15% slightly faster (6.5–8.4 S) sedimenting material (see Fig. 1c). This is most likely the result of some nonspecific association between pentamers and some improperly folded monomers. When a nucleoplasmin solution was mixed with 0.5 mol of histone of nucleoplasmin this in a sedimentation coefficient from 6.5 to S (see Fig. of histone octamer to a of mol of of nucleoplasmin pentamer a of the sedimentation coefficients in which for the in extinction coefficients of nucleoplasmin and the histone of the with a sedimentation coefficient at the as histones (see Fig. Sedimentation equilibrium analysis of the consisting of complex an average molecular weight of which is in very with that of histones to a to nucleoplasmin in a in which the of material sedimenting as histones (see Fig. for the in extinction coefficients of nucleoplasmin and This value is in very with the value calculated in the that mol of nucleoplasmin binds to mol of histone In these the average sedimentation coefficient of the sedimenting corresponding to the complex exhibits a to decrease as the from 0.5 to of equivalent histone of nucleoplasmin (see Fig. This is most likely to the of sedimenting histones. of the results of the shown in Fig. indicate that each nucleoplasmin pentamer is to bind one histone octamer of Core Histones to Nucleoplasmin Core Histone results not us to the different histone domains dimer and H3-H4 bind to the nucleoplasmin pentamer with the same or is any preference for one of the nucleoplasmin pentamer is to an of histone To this and to the analytical ultracentrifuge we carried out a histone to nucleoplasmin using sucrose gradients and analyzed the protein composition of the corresponding to the using SDS-PAGE can be of nucleoplasmin pentamers with a stoichiometric of histone octamers in a , that sediments slightly than nucleosome core 20,w = ± r = (16Ausió J. Dong F. van Holde K.E. J. Mol. Biol. 1989; 206: 451-463Crossref PubMed Scopus (282) Google Scholar) run under the same conditions , and faster than the nucleoplasmin pentamer , When the same was carried out using a of histone octamers mol of histone of nucleoplasmin two were obtained , The faster one with the corresponding to the stoichiometric for the in extinction coefficient of the histone octamer and the of the was determined to be of that of the faster on the of mol of nucleoplasmin binding mol of histone the of the core histones was the same in both not the histone the main polyglutamic tract of nucleoplasmin the binding of histones to It is possible to remove the highly positively charged N-terminal domains of histones by treatment of nucleosome with immobilized trypsin (16Ausió J. Dong F. van Holde K.E. J. Mol. Biol. 1989; 206: 451-463Crossref PubMed Scopus (282) Google Scholar) by hydroxylapatite to remove the The treatment not the histone which is responsible for the of the histone and it not have on the of the histone When a nucleoplasmin solution was with amounts of trypsinized histone the sedimentation of the (see Fig. was very to that observed for native histone octamers (see Fig. A boundary corresponding to for in extinction of histones is observed a of mol of nucleoplasmin was with 2 mol of trypsinized histone octamers (see Fig. which is slightly than the this complex was analyzed in a sucrose gradient (see Fig. of the mixture as a The as a for which the with that of a complex consisting of mol of of trypsinized histones and an molecular weight by sedimentation equilibrium of The trypsinized histone nature of the sedimenting and the histone composition of both was by SDS-PAGE analysis (see Fig. This analysis that as with the native histones, the faster sedimenting to the has histone to the role of the C-terminal polyglutamic tract of nucleoplasmin in the formation of the this of nucleoplasmin is highly negatively charged under physiological it be to play a major role in the formation of the complex with the positively charged histones. shown in Fig. removal of the polyglutamic tract any on histone of nucleoplasmin not the formation of a pentameric which sediments with an average sedimentation coefficient of ± 0.1 S (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar). of histone the in a way that is also very to that of the native complexes. of the histones as histones 2 mol of histones are mixed with mol of nucleoplasmin (see Fig. a value that is in with that The complex sediments with an average sedimentation coefficient of 10 ± 0.1 which is from that of the native a that in this most likely the decrease in the of the nucleoplasmin pentamer upon removal of the C-terminal domains of the (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar). In the nucleoplasmin of Laskey and S.M. S.J. Laskey R.A. Cell. Full Text PDF PubMed Scopus Google Scholar), it was shown that this molecule a histone complex with histones and The of this protein in removal of the sperm-specific proteins and of the male pronuclear chromatin was A. Leno G.H. Cell. 1992; 69: 759-767Abstract Full Text PDF PubMed Scopus (195) Google and 10Laskey R.A. Mills A.D. Philpott A. Leno G.H. Dilworth S.M. Dingwall C. Philos. Trans. R. Soc. Lond.-Biol. Sci. 1993; 339: 263-269Crossref PubMed Scopus (58) Google Scholar). A model was in which histone H2A-H2B dimers were to the histone chromatin of X. laevis Histones and Inc., Scholar) upon removal of the sperm-specific proteins. proteins an chromatin that to be by nucleosomes of a of histones H2A, H2B, H3, and nucleoplasmin has been shown to be the major protein of the of other such as the protein composition of protamines K. Katagiri C. Dev. Biol. 1991; 148: 295-305Crossref PubMed Scopus (71) Google Scholar). nucleoplasmin in the of histones has been shown to be to chromatin remodeling of protamine containing chromatin T. K. Katagiri Dev. 1993; Scopus Google Scholar) or DNA A. Eur. J. Biochem. PubMed Scopus (13) Google Scholar). These that in to a role for histones and H2B, nucleoplasmin may also be to bind to a core histone complement and in this way in the process of nucleosome early A of nucleoplasmin from X. laevis and a protein from has been and a model has been on this for the possible interactions with the histone octamer S. Akey I.V. Dingwall C. Hartman K.L. Laue T. Nolte R.T. Head J.F. Akey C.W. Mol. Cell. 2001; 8: 841-853Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 7Akey C.W. Luger K. Curr. Opin. Struct. Biol. 2003; 13: 6-14Crossref PubMed Scopus (162) Google Scholar, 8Namboodiri V.M.H. Dutta S. Akey I.V. Head J.F. Structure. 2003; 11: 175-186Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar). to this histone octamers bind to a nucleoplasmin a nucleoplasmin has been observed in solution (15Prieto C. Saperas N. Arnan C. Hills M.H. Wang X. Chiva M. Aligue R. Subirana J.A. Ausió J. Biochemistry. 2002; 41: 7802-7810Crossref PubMed Scopus (24) Google Scholar). under the ionic strength conditions in those to their m NaCl) under those used to mm NaCl) S. Akey I.V. Dingwall C. Hartman K.L. Laue T. Nolte R.T. Head J.F. Akey C.W. Mol. Cell. 2001; 8: 841-853Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 8Namboodiri V.M.H. Dutta S. Akey I.V. Head J.F. Structure. 2003; 11: 175-186Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar) core histones exist as an for that model to be it also to be that nucleoplasmin the of the histone octamer under those ionic a that to be The results in this under ionic physiological conditions the histone octamer is in equilibrium with the histone H3-H4 tetramer and the histone H2A-H2B dimer (3Eickbush T.H. Moudrianakis E.N. Biochemistry. 1978; 17: 4955-4964Crossref PubMed Scopus (273) Google Scholar) (see Fig. indicate that one histone octamer equivalent binds a nucleoplasmin The of a at ratios of in all of the that the histone octamers not bind octamers as H2A-H2B dimers and H3-H4 (see Fig. The of the of interaction observed both in the absence of the histone and in the absence of the polyglutamic C-terminal of nucleoplasmin that these highly charged domains play a role in the interaction and that the place between the folded of the nucleoplasmin pentamer S. Akey I.V. Dingwall C. Hartman K.L. Laue T. Nolte R.T. Head J.F. Akey C.W. Mol. Cell. 2001; 8: 841-853Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar) and the histone (2Luger K. Mader A.W. Richmond R.K. Sargent D.F. Richmond T.J. Nature. 1997; 389 (226): 251Crossref PubMed Scopus (6830) Google Scholar, 26Arents G. Moudrianakis E.N. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 11170-11174Crossref PubMed Scopus (287) Google Scholar) as indicated in Fig. can be in Fig. the complex between the nucleoplasmin pentamer and the histones exhibits a slightly sedimentation coefficient value ± S) the decrease in molecular than that of the complex with histones, a that the of the complex from the removal of the histone (see Fig. the in analysis of the interaction between nucleoplasmin and core histones not show any preference of nucleoplasmin by any of core histones, which are all in stoichiometric in the complexes. Xenopus as other and invertebrate amounts of histones in their These histones are involved in the chromatin remodeling that takes place immediately after fertilization in those organisms in which chromatin of protamines and sperm-specific proteins. In two have been from consisting of H2A-H2B and nucleoplasmin and histone H3-H4 in association of a of and J.A. Cell. 1982; Full Text PDF PubMed Scopus Google Scholar). nucleoplasmin is by the most abundant protein in Xenopus (10Laskey R.A. Mills A.D. Philpott A. Leno G.H. Dilworth S.M. Dingwall C. Philos. Trans. R. Soc. Lond.-Biol. Sci. 1993; 339: 263-269Crossref PubMed Scopus (58) Google Scholar), and a of histones has also been to be to it in S from these by sucrose gradients J.A. G. H. J. Biol. Chem. Full Text PDF PubMed Google Scholar). Although the of the S in this to the S by et al. J.A. G. H. J. Biol. Chem. Full Text PDF PubMed Google Scholar) is not the of four core histones in this to the that nucleoplasmin can in the of nucleosomes in T. K. Katagiri Dev. 1993; Scopus Google Scholar, T. M. R. J.T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The results described in this using of H2A-H2B and histone H3-H4 and the with which bind to nucleoplasmin have for the way nucleoplasmin at the level of in the that nucleoplasmin in in the nucleosome after removal of the sperm-specific proteins from the male pronuclear chromatin for with the analytical for in the and J. A. Subirana for

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