![]() ![]() PEARSON PROTEIN SCAFFOLD CHROMOSOME FREEOne 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. The study of chromosome banding at higher resolution has been another field of study, exemplified by preparations of prophase chromosomes with several times as many bands as in metaphase chromosomes, and also by the application of electron microscopy to banded chromosomes.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). As a by-product of this technique, the induction of sister chromatid exchanges by radiation or chemicals has been adopted as a sensitive test for mutagens. Using bromodeoxyuridine substitution, the replication of chromosomes can now be studied with great precision. The technique of in situ hybridization has been refined so that single genes can be located on chromosomes similarly, immunocytochemistry is being used to investigate the distribution of specific proteins on chromosomes. Other staining techniques have aimed to provide greater specificity for parts of chromosomes such as the kinetochore and nucleolar organizing regions. Silver staining of the synaptonemal complex, a structure which may be a meiotic equivalent of the scaffold, is assisting greatly in studies of chromosome pairing. The Scaffold Model of chromosome structure represents the chromosome as a proteinaceous core from which radiate loops of deoxyribonucleoprotein. A variety of new concepts and techniques, and refinements of existing techniques, are being used to attack a number of problems of chromosome organization. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |