Histones

M.p. 207°C. The naturally occurring substance is dextrorotatory. Arginine is one of the essential amino-acids and one of the most widely distributed products of protein hydrolysis. It is obtained in particularly high concentration from proteins belonging to the prolamine and histone classes. It plays an important role in the production of urea as an excretory product. 

CfiHqNaO . M.p. 277 C. The naturally occurring substance is laevorotatory. Histidine is one of the basic amino-acids occurring in the hydrolysis products of proteins, and particularly of the basic proteins, the protamines and histones. It is an essential constituent of the food of animals. 

H2N-CH2 [CH2j3.CH(NH2) COOH. Colourless needles, m.p. 224 C (decomp.), very soluble in water, insoluble in alcohol. L-(-H)-Lysine is one of the basic amino-acids occurring in particularly large quantities in the protamine and histone classes of proteins. It is an essential amino-acid, which cannot be synthesized by the body and must be present in the food for proper growth. It can be manufactured by various fermentation processes or by synthesis. 

Nucleoproieins. The prosthetic group of the nucleoproteins is nucleic acid, often linked through salt linkages with protamines or histones. The nucleoproteins are present in the nuclei of all cells. Chromasomes are largely nucleoproteins and some plant viruses and bacteriophages have been shown to be pure nucleoproteins. See also histones. 

FIGURE 28 6 The effective length of DNA is reduced by coiling around the surface of histones to form nucleo somes The histone proteins are represented by the spheres and the DNA double helix by the ribbon... 

Section 28 9 Within the cell nucleus double helical DNA adopts a supercoiled terti ary structure m which short sections are wound around proteins called histones This reduces the effective length of the DNA and maintains it m an ordered arrangement... 

Heterogeneous reaction (Section 6 1) A reaction involving two or more substances present in different phases Hydro genation of alkenes is a heterogeneous reaction that takes place on the surface of an insoluble metal catalyst Heterolytic cleavage (Section 4 16) Dissociation of a two electron covalent bond in such a way that both electrons are retained by one of the initially bonded atoms Hexose (Section 25 4) A carbohydrate with six carbon atoms High density lipoprotein (HDL) (Section 26 11) A protein that carries cholesterol from the tissues to the liver where it is metabolized HDL is often called good cholesterol Histones (Section 28 9) Proteins that are associated with DNA in nucleosomes... 

More subtle modes of action are also possible since the response to hormone receptor binding is complex and could be affected by chemical interference with receptor-related proteins, DNA methylation or histone acetylation. Dioxin (TCDD), for example, reduces the ability of the oestrogen-receptor complex to bind to the oestrogen response element of DNA, reducing gene transcription. ... 

Histones (from S4A mouse lymphoma). Purification used a macroprocess column, heptafluorobutyric acid as solubilising and ion-pairing agent and an acetonitrile gradient. [McCroskey et al. Anal Biochem 163 427 1987.]... 

Toyopearl HW-50S resin has been used to help isolate the ubiquitin-histone conjugate mH2A from the unicellular ciliated protozoan Tetrahymena pyriformis. Figure 4.49 shows the separation of mH2A from the histone, H2A. The sole difference between these two components is a small polypeptide, ubiquitin (approximately 8500 Da). The mH2A fraction was then further purified by HPLC on a Tosoh ODS-silica column (52). One of the many benefits... 

FIGURE 4.49 Isolation of a complex protein conjugate on Toyopearl HW-50S. Column 22 mm X 83 cm. Sample Fraction from crude Tetrahymena H2A containing the ubiquitin-histone conjugate uH2A. Elution 10 nM HCI. Flow rate 0.1 ml/min. Detection UV at 230 nm. 

Histones (Section 28.9) Proteins that are associated with DNA in nucleosomes. 

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. 

Histone core octamer (here shown in cross section)... 

FIGURE 11.23 A diagram of the histone octamer. Nucleosomes consist of two turns of DNA supercoiled about a histone core octamer. 

Histone Ratio of Lysine to Arginine M, Copies per Nucleosome... 

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. 

If chromatin is swelled suddenly in water and prepared for viewing in the electron microscope, the nucleosomes are evident as beads on a string, dsDNA being the string (Figure 12.28). The structure of the histone octamer core has been determined by X-ray crystallography without DNA by E. N. Moudrianakis s laboratory (Figure 12.29) and wrapped with DNA by T. J. 

Richmond and collaborators (Figure 12.30). The octamer (Figure 12.29) has surface landmarks that guide the course of the DNA around the octamer 146 bp of B-DNA in a flat, left-handed superhelical conformation make 1.65 turns around the histone core (Figure 12.30), which itself is a protein superhelix consisting of a spiral array of the four histone dimers. Histone 1, a three-domain protein, serves to seal the ends of the DNA turns to the nucleosome core and to organize the additional 40 to 60 bp of DNA that link consecutive nucleo-... 

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. 

American Chemical. Society. (1996). A Mational Histone Chemical Landmark The Houdry Process for the Catalytic Conversion of Crude Petroleum to I ligh-Octane Gasoline. Washington, DC American Chemical Society. Buonora, P. T. (1998). Aimer IVicAfee at Gulf Oil. Chemical Heritage 16(2) 5-7, 44—4G. 

Haensel, V. (1983). The Development of the Platforming Process—.Some Personal and Catalytic Recollections. In Heterogeneous Catalysis Selected American Histones, eds. B. H. Davis and W. P. Hettinger. Aiiiericaii Clieiiiical Society. Symposium Series No. 222. Washington, DC American Chemical Society. 

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