![]() Tavormina, P.A., Come, M.G., Hudson, J.R., Mo, Y.Y., Beck, W.T., and Gorbsky, G.J., Rapid Exchange of Mammalian Topoisomerase IIα at Kinetochores and Chromosome Arms in Mitosis, J. 775–785.Ĭhristensen, M.O., Larsen, M.K., Barthelmes, H.U., Hock, R., Andersen, C.L., Kjeldsen, E., Knudsen, B.R., Westergaard, O., Boege, F., and Mielke, C., Dynamics of Human DNA Topoisomerases IIα and IIβ in Living Cells, J. Kireeva, N., Lakonishok, M., Kireev, I., Hirano, T., and Belmont, A.S., Visualization of Early Chromosome Condensation: a Hierarchical Folding, Axial Glue Model of Chromosome Structure, J. and Laemmli, U.K., A Two-Step Scaffolding Model for Mitotic Chromosome Assembly, Dev. Structure of Isolated Protein-Depleted Chromosomes, Chromosoma, 1981, vol. Hadlaczky, G., Sumner, A.T., and Ross, A., Protein-Depleted Chromosomes. and Laemmli, U.K., The Structure of Histone Depleted Metaphase Chromosomes, Cell, 1977, vol. Razin, S.V., Chromosomal DNA Loops May Constitute Basic Units of the Eukaryotic Genome Organization and Evolution, Crit. Černá, A., López-Fernández, C., Fernández, J.L., Moreno Díaz de la Espina, S., de la Torre, C., and Gosálvez, J., Triplex Configuration in the Nick-Free DNAs That Constitute the Chromosomal Scaffolds in Grasshopper Spermatids, Chromosoma, 2008, vol. and Polyakov, V.Y., Chromosome Scaffold and Structural Integrity of Mitotic Chromosomes, Russian J. Tsutsui, K.M., Sano, K., and Tsutsui, K., Dynamic View of the Nuclear Matrix, Acta Medica Okayama, 2005, vol. Karsenti, E., Self-Organization in Cell Biology: a Brief History, Nat. Misteli, T., Physiological Importance of RNA and Protein Mobility in the Cell Nucleus, Histochem. Harold, F.M., Molecules into Cells: Specifying Spatial Architecture, Microbiol. Gorski, S.A., Dundr, M., and Misteli, T., The Road Much Traveled: Trafficking in the Cell Nucleus, Curr. The residual structures may be considered as a “snapshot” of all proteins transiently (or statically) bound to their target sites at the moment of permeabilization. One may suppose that the protein fraction associated with residual structures includes molecules interacting with their binding sites at the moment of permeabilization, while the free proteins are extracted (i.e., during the interaction with binding sites, these proteins form salt-resistant complexes however, on diffusion the same proteins are extractable by the high-salt solution). However, in most cases it remains possible to extract a structurally visible protein fraction with 2 M NaCl (protein distributed in nucleoplasm). Both pKi-67 and B23 remain associated with the nuclear matrix even when they are translocated to nucleoplasmic foci due to inhibitor action or hypotonic treatment. The results show that these two proteins are associated with residual structures throughout the cell cycle only those structures change that contain proteins precipitated by 2 M NaCl (nucleoli, perichromosomal layer, prenucleolar bodies, cytoplasm of mitotic cells). In the present paper, we have analyzed the association of two perichromosomal layer proteins, pKi-67 and B23, with the residual structures. This contradiction between predicted stability and observed dynamics led us to reexamine the principles underlying the association of proteins with residual structures. However, in vivo microscopy has recently revealed that the components of these “static” structures are highly mobile and continuously exchanged between specific target sites and the nucleoplasm or cytoplasm. According to the radial loop model of chromosome organization, a major role in the formation and maintenance of chromosomes is played by the residual structures (the nuclear matrix in interphase nuclei and the chromosome scaffold in metaphase chromosomes).
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