ABSTRACT
In the present review the structural role of noncoding DNA, mechanisms of differential staining of mitotic chromosomes, and structural organization of different levels of DNA compactization are discussed. A structural-functional model of the mitotic chromosome is proposed based on the principle of discreteness of structural levels of DNA compactization.
Subject(s)
Chromosomes, Human/chemistry , Chromosomes, Human/metabolism , Chromosomes/chemistry , Chromosomes/metabolism , Mitosis , Animals , Calcium/metabolism , Chromatin/chemistry , Chromatin/ultrastructure , Chromosomal Proteins, Non-Histone/chemistry , Chromosomal Proteins, Non-Histone/metabolism , Chromosomes/ultrastructure , Chromosomes, Human/ultrastructure , DNA/chemistry , Euchromatin/chemistry , Euchromatin/metabolism , Heterochromatin/chemistry , Heterochromatin/metabolism , Histones/chemistry , Histones/metabolism , Humans , InterphaseABSTRACT
Individual mitochondria which form the chondriom of eucaryotic cells are highly dynamic systems capable of fusion and fragmentation. These two processes do not exclude one another and can occur concurrently. However, fragmentation and fusion of mitochondria regularly alternate in the cell cycle of some unicellular and multicellular organisms. Mitochondrial shapes are also described which are interpreted as intermediates of their "equational" division, or fission. Unlike the fragmentation, the division of mitochondria, especially synchronous division, is also accompanied by segregation of mitochondrial genomes and production of specific "dumbbell-shaped" intermediates. This review considers molecular components and possible mechanisms of fusion, fragmentation, and fission of mitochondria, and the biological significance of these processes is discussed.
Subject(s)
Intracellular Membranes/physiology , Membrane Fusion/physiology , Mitochondria/physiology , Animals , Cell Cycle/physiology , Gene Expression Regulation, Fungal/physiology , Microtubules/physiology , Mitochondria/ultrastructure , Mitochondrial Proteins/physiology , Saccharomyces cerevisiae/physiology , Saccharomyces cerevisiae/ultrastructureABSTRACT
The method of chromatin photo-stabilization by the action of visible light in the presence of ethidium bromide was used for investigation of higher-level chromatin structures in isolated nuclei. As a model we used rat hepatocyte nuclei isolated in buffers which stabilized or destabilized nuclear matrix. Several higher-level chromatin structures were visualized: 100nm globules-chromomeres, chains of chromomeres-chromonemata, aggregates of chromomeres-blocks of condensed chromatin. All these structures were completely destroyed by 2M NaCl extraction independent of the matrix state, and DNA was extruded from the residual nuclei (nuclear matrices) into a halo. These results show that nuclear matrix proteins do not play the main role in the maintenance of higher-level chromatin structures. Preliminary irradiation led to the reduction of the halo width in the dose-dependent manner. In regions of condensed chromatin of irradiated nucleoids there were discrete complexes consisting of DNA fibers radiating from an electron-dense core and resembling the decondensed chromomeres or the rosette-like structures. As shown by the analysis of proteins bound to irradiated nuclei upon high-salt extraction, irradiation presumably stabilized the non-histone proteins. These results suggest that in interphase nuclei loop domains are folded into discrete higher-level chromatin complexes (chromomeres). These complexes are possibly maintained by putative non-histone proteins, which are extracted with high-salt buffers from non-irradiated nuclei.
