Electrochemical study of mononucleosome

The electrochemical behavior of mononucleosome has been studied in parallel with circular dichroism and trypsin degradation. In mononucleosome, DNA is never adsorbed at the electrode surface. A model of flat adsorption of the mononucleosome via histones is proposed.     

Chromatin organization at meiosis

From 1956, when the complex ultrastructure of meiotic chromosomes was discovered, ¹ until 1985, when the isolation of meiotic chromosome cores was reported, knowledge of the molecular structure of the meiotic chromosome was at best a dream. The dissection of meiotic chromosome structures has become a realistic challenge through the arrival of isolated symptonemal complexes (SCs), monoclonal and polyclonal antibodies against SCs, the possibility for screening expression libraries for genes that encode SC proteins, the isolation of SC-associated DNA, and the development of techniques for the in situ recognition of DNA sequences in the context of the meiotic chromosome structure.     

Chromatin organization in rat testis nuclei. Flow cytometric detection of the morphological compaction

The unusual histone composition of testicular cells generates changes in chromatin organization in order to allow the chromosomal pairing necessary for genetic recombination. Accessibility of testis nuclear DNA was determined by flow cytometry. The observed differences in staining between testis and liver nuclear chromatin, as well as the differences of perpendicular light scatter signal, correlate with alterations in protein composition with the chromatin reorganization.     

Overall pathway of mononucleosome production.

Five electrophoretically distinguishable classes of mononucleosomes (MI, MII, ...MV) are produced upon treatment of mammalian nuclear chromatin with micrococcal nuclease. These five forms differ in their initial DNA lengths, relative mass proportions, stability, contents of histone H1, and presence of certain nonhistone proteins. A new "chromatin fingerprinting" technique has been developed in order to trace nuclease-mediated interconversions between these mononucleosomes and their polynucleosomal precursors. Application of this technique, together with earlier findings from this laboratory, has made possible the elucidation of the overall pathway of nuclease cleavage of chromatin which leads to the production and interconversion of these mononucleosomes, and has permitted reconstruction of the organization of these mononucleosomes in undigested chromatin...     

Chromatin compaction and the efficiency of formation of DNA-protein crosslinks in gamma-irradiated mammalian cells.

Chromatin has been prepared from Chinese hamster V79 cell nuclei by successive suspension and sedimentation in buffers of decreasing ionic strength. For buffer concentrations from 50 to 1 mM, the resultant chromatin maintained a normal histone content, nucleosomal organization, and attachment to the nuclear matrix; however, as the buffer concentration was reduced from 50 to 10 and 1 mM, the higher-order chromatin structures became increasingly relaxed. Fully expanded chromatin is 5- to 10-fold more susceptible to the induction of DNA-protein crosslinks (DPCs) by gamma radiation than is chromatin residing in living interphase cells. As much as 60-70% of expanded chromatin can be induced to form DPCs as compared to a maximum of about 20% of cellular DNA. For expanded chromatin, the maximum level of induced DPCs is two to three times higher than would be expected if only matrix-associated DNA were induced to form DPCs. Therefore, DNA in distal regions of chromatin loops must also be induced to form DPCs with histones or other nonhistone chromosomal proteins. The hypersensitivity of isolated chromatin to radiation-induced production of DPCs appears to be related to the expansion of chromatin conformation rather than to the removal of intracellular radical scavengers for the following reasons: (a) there is an inverse relationship between the buffer concentration in which the chromatin is suspended and DPC formation, and (b) the induction of a more compact 30-nm chromatin fiber from the expanded 10-nm chromatin fiber in the presence of a low concentration of MgCl2 results in a marked reduction in DPC formation. The formation of radiation-induced DPC seems to occur at maximum efficiency in fully expanded chromatin, since DPC formation cannot be further stimulated by the addition of Cu2+, which can catalyze the production of OH by Fenton chemistry. It is concluded that radiation-induced DNA damage production is greatly influenced by chromatin conformation, and that chromatin as it exists in the cell is a relatively poor substrate for DNA-protein crosslinking in comparison to completely expanded chromatin.     

Chromatin remodeling: nucleosomes bulging at the seams

ATP-dependent chromatin remodeling enzymes, such as SWI/SNF, hydrolyze thousands of ATPs to regulate gene expression on chromatin fibers. Recent mechanistic studies suggest that these enzymes generate localized changes in DNA topology that drive formation of multiple, remodeled nucleosomal states.     

Chromatin: bind at your own RSC

Recent work has identified a novel RSC-nucleosome complex that both strongly phases flanking nucleosomes and presents regulatory sites for ready access. These results challenge several widely held views.     

Chromatin diminution at the border of the XX and XXI centuries

The size of genomes in eukaryotic organisms is one of the greatest mysteries of biology. As known from the middle of the XX century, the level of organization of a particular organism, does not depend on its genome size, i. e. on DNA amount in the nucleus. We believe that an actual function of non-coding DNA stands behind the phenomenon of chromatin diminution, known already for 100 years. Diminution of chromatin normally takes place in cells involved in body building and never occurs in developmental precursors of germ cells. Apparently, the former are cells, in which non-coding DNA is functionally significant. We cloned a fraction of DNA eliminated during chromatin diminution of Cyclops kolensis (Cyclopoida, Crustascea) and sequenced 90 clones totally making 32 kb. Taken together, the provided evidence has demonstrated a high organization ordering of DNA sequences restricted to the germ line. Chromatin diminution never takes place in human cells and in cells of the majority of animals. These cells may isolate non-coding DNA in other ways, making it unreactable for most enzymes and thus functionally cut off. Thus, a certain part of genome with a particular size and structure may serve for genetic isolation of species as shellfish or junk DNA are vital components rather than pieces of garbage.