Chromosomes Histones

Two-dimensionai gel electrophoresis of histones from interphase and mitotic cells treated with dimethyl sulfate. 2-D gel electrophoresis was carried out with proteins separated by nonequilibrium pH gradient electrophoresis in the first dimension and on 8% polyacrylamide slab gels in the second (6, 7). Separation of histones was enhanced by use of a urea solubilization buffer containing protamines to displace histones from DNA (8). The resulting autoradiograms for histones of both nuclei and chromosomes are in Fig. 3. Incubation of mitotic cells with [32P]NAD before chromosomes were isolated led to prominent labeling of histones H2B and H4 (A, B), and spots are also visible at the positions of HIA and HIB. 32p incorporation is also seen at the positions of histones H2A and H3. hi Fig. 3B, a similar pattern is observed for chromosomal histones from cells treated with DMS. The primary acceptors of isotope are H2B and H4, with radioactivity also present at the positions of HIA, HIB, H2A, and H3. A major change in the relative distribution of 32p between species is clearly not a feature of DMS treatment. 

Imaging/Labeling Applications Amines/amino groups antibodies cells chromosomes histone deacetylases liposomes nanoparticles nucleic acids/nucleotides polymersomes ... 

Imaging/Labeling Applications Antibodies blood vessels ceUs " chromosomes histone deacetylases proteins tetanus toxin (TTc) ... 

Imaging/Labeling Applications Antibodies, " bacteria chromosomes histone deacetylase Hodgkin and Reed Sternberg (HRS) cells microorganisms nucleotides/nucleic acids peptides/proteins silver particles T lymphoc5de antigens " ... 

Nucleus The nucleus is separated from the cytosol by a double membrane, the nuclear envelope. The DNA is complexed with basic proteins (histones) to form chromatin fibers, the material from which chromosomes are made. A distinct RNA-rich region, the nucleolus, is the site of ribosome assembly. The nucleus is the repository of genetic information encoded in DNA and organized into chromosomes. During mitosis, the chromosomes are replicated and transmitted to the daughter cells. The genetic information of DNA is transcribed into RNA in the nucleus and passes into the cytosol where it is translated into protein by ribosomes. 

Histone H3 Histones are DNA-binding proteins found in chromosomes 135 amino acid residues. Note die very basic nature of this protein dne to its abmidance of Arg and Lys residues. It also lacks tryptophan. 

The DNA in a eukaryotic cell nucleus during the interphase between cell divisions exists as a nucleoprotein complex called chromatin. The proteins of chromatin fall into two classes histones and nonhistone chromosomal proteins. 

FIGURE 12.31 A model for chromosome structure, human chromosome 4. The 2-um DNA helix is wound twice around histone octamers to form 10-um uucleosomes, each of which contains 160 bp (80 per turn). These uucleosomes are then wound in solenoid fashion with six uucleosomes per turn to form a 30-nm filament. In this model, the 30-nm filament forms long DNA loops, each containing about 60,000 bp, which are attached at their base to the nuclear matrix. Eighteen of these loops are then wound radially around the circumference of a single turn to form a miniband unit of a chromosome. Approximately 10 of these minibands occur in each chromatid of human chromosome 4 at mitosis. 

Histone phosphorylation is a common posttranslational modification fond in histones, primarily on the N-terminal tails. Phosphorylation sites include serine and threonine residues, tyrosine phosphorylation has not been observed so far. Some phosphorylation events occur locally whereas others occur globally throughout all chromosomes during specific events like mitosis. Histone phosphorylation is catalyzed by kinases. Removal of the phosphoryl groups is catalyzed by phosphatases. 

Acetylation of core histones is associated with chromosomal assembly during DNA replication. 

Phosphorylation of histone HI is associated with the condensation of chromosomes during the replication cycle. 

The double-helical DNA is packaged into a more compact structure by a number of proteins, most notably the basic proteins called histones. This condensation may serve a regulatory role and certainly has a practical purpose. The DNA present within the nucleus of a cell, if simply extended, would be about 1 meter long. The chromosomal proteins compact this long strand of DNA so that it can be packaged into a nucleus with a volume of a few cubic micrometers. 

Most of the DNA of animal cells is found in the nucleus, where DNA is the major constituent of the chromosomes. On the other hand, most of the RNA is located in the cytoplasm. Nuclear DNA exists as a thin, double helix only 2 nm wide. The double helix is folded and complexed with protein to form chromosomal strands approxim-ately 100 to 200 nm in diameter. Each chromosome contains a single DNA duplex. The human chromosomes vary in size the smallest contains approximately 4.6 X 10 base pairs of DNA, and the largest 2.4 X 10 base pairs. In contrast, the Escherichia coli chromosome has 4.5 x 106 base pairs. The DNA of die chromosomes is tightly packed and associated with both histone and nonhistone proteins. 

The nucleus contains a large number of proteins other than histones. These so-called nonhistone proteins may or may not be tightly associated with the chromosomes. For example, the nucleus contains enzymes associated with the synthesis of RNA and DNA these are nonhistone proteins, but they are not part of the structure of chromosomes. One group of nonhistone proteins are the high mobility group (HMG) proteins, named for their rapid movement on polyacryl-amide gel electrophoresis. The HMG proteins, but not histone HI, are associated with the chromatin that is most active in RNA synthesis. 

Bacteria normally harbour a single, circular chromosome that tends to be tethered to the bacterial plasma membrane and tends to have few if any closely associated proteins. Many bacteria also contain extra-chromosomal DNA in the form of plasmids, as will be discussed later. Eukaryotes (plants, animals and yeasts) posses multiple linear chromosomes contained within a cell nucleus, and these chromosomes are normally closely associated with proteins termed histones (the pro-tein-DNA complex is termed chromatin). Eukaryotes also invariably possess DNA sequences within mitochondria and in chloroplasts in plants. The (usually circular) DNA molecules are much... 

Binding of nitroso-procainamide to histone proteins may perturb chromatin structure or catabolism, resulting in immunogenic forms of DNA-free histones. In fact, all sera of patients (n = 24) with procainamide-induced Lupus showed IgG and IgM antibody activity against various histone components of chromatin (chromosome subunits)122. The nature of the procainamide adduct to histone proteins still awaits elucidation. 

In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. 

DMA and histone proteins are packaged into structures called chromosomes. 

Chromatin The material of chromosomes. It is a complex of DNA, histones, and nonhistone proteins (chromosomal proteins, non-histone) found within the nucleus of a cell. [NIH]... 

Histones Small chromosomal proteins (approx 12-20 kD) possessing an open, unfolded structure and attached to the DNA in cell nuclei by ionic linkages. Classification into the various types (designated histone I, histone II, etc.) is based on the relative amounts of arginine and lysine in each. [NIH]... 

Histone HI can be modified through phosphorylation (Langan and Hohmann, 1975). A change in the extent of HI phosphorylation was correlated with the onset of mitosis (Lake and Salzman, 1972) and it has been suggested that this serves as a trigger for chromosome con-... 

Goldknope, I. L. and Busch, H. Isopeptide linkage between nonhistone and histone 2A polypeptides of chromosomal conjugate-protein A24. Proc. Natl. Acad. USA, 1977, 74, 864-868. 

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