Histone protein

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... 

Due to the large amount of DNA present within the nucleus it must be carefully packaged. In the resting cell DNA is tightly compacted around basic histone proteins, excluding the binding of the enzyme RNA polymerase II, which activates the formation of mRNA. This conformation of the chromatin structure... 

Histone acetylation is a reversible and covalent modification of histone proteins introduced at the e-amino groups of lysine residues. Histones and DNA form a complex - chromatin - which condenses DNA and controls gene activity. Current models interpret histone acetylation as a means to regulate chromatin activity. 

Histone proteins share distinct features including a high content of basic amino acids, lysines and arginines,... 

In the nucleosome, the DNA is supercoiled in a left-handed helix over the surface of the disk-shaped histone octamer (Figure 36-2). The majority of core histone proteins interact with the DNA on the inside of the supercoil without protruding, though the amino terminal tails of all the histones probably protrude outside of this structure and are available for regulatory covalent modifications (see Table 36-1). 

Much of the DNA is associated with histone proteins to form a structure called the nucleosome. Nucleo-somes are composed of an octamer of histones and 150 bp of DNA. 

Abstract Histone proteins that form the nucleosome core are subject to a variety of post-translational... 

In the nuclei of all eukaryotic cells, DNA is tightly wrapped around an octamer of histone proteins and is compacted into a dense structure known as chromatin. In order to access the genetic information which is required in numerous essential cellular processes including DNA replication, gene expression and DNA repair, chromatin needs to be partially unwound. One important mechanism to regulate chromatin structure and thus to control the access of the genomic DNA is through histone modifications [1-6]. The histone octamer is composed of two copies of H2A, H2B, H3 and H4 core histone proteins. Their tails, that protrude out of the surface of the... 

SADP or sulfo-SADP also have been used to study the phenylalanine-methionine-arginine-phenylalanine-amide-activated sodium channel (Coscoy et al., 1998), various apolipoprotein E isoforms (Mann et al., 1995), the high-affinity phenylalkylamine Ca2+ antagonist binding protein from guinea pig (Moebius et al., 1994), the interaction of non-histone proteins with nucleosome core particles (Reeves and Nissen, 1993), and the interactions among cytochromes P-450 in the endoplasmic reticulum (Alston et al., 1991). See Chapter 28 for methods of using photoreactive heterobifunctional crosslinkers to study protein interactions. 

Binding of A-hydroxy-procainamide (in the presence of oxygen) to histone proteins of white blood cells was markedly reduced by ascorbic acid, but the material bound was not liberated by acid treatment120,122. Hence, it was suggested by the authors that nitroso-procainamide may have reacted with something other than sulfliydryl groups, particularly since histone proteins contain very few sulfhydryl groups60,120,122. 

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. 

DMA and histone proteins are packaged into structures called chromosomes. 

Furthermore, there is a striking parallelism between these data and the neutron diffraction data from nucleosomes in 100% D 0 (Pardon et al., 1977 Suau et al., 1977), where scattering from the histone protein dominates, and from core protein in 2 M NaCl solution (Pardon et al., 1978). The above interference phenomenon may well be the explanation for the protein-dominated scattering maximum between 35 and 37 A observed for chromatin and nucleosomes in solution (Pardon et al., 1977 Suau et al., 1977). 

Another group of non-histone proteins have been identified as essential components for the formation of the condensed chromosome (Table 1). Topoisomerase II (topo II) localizes in the scaffold/matrix fraction of the interphase nuclear (Berrios et al., 1985) and the mitotic chromosome (Maeshima and Laemmli, 2003) (see section 3.1). Topo II forms a ring-shaped homodimer (Berger et al, 1996 Nettikadan et al, 1998) and catalyzes the decatenation and relaxation of DNA double strand (Wang, 2002). In fission yeast, chromosomes cannot be condensed without functional topo II (Uemura et al, 1987). In addition, in in vitro experiment, mitotic extracts containing topo II induce chromatin condensation in the isolated nuclei from HeLa and chicken erythrocyte cells (Adachi et al., 1991). 

DNA is packaged in the nucleus into the form of chromatin. Chromatin is a nucleoprotein complex composed of histone and non-histone proteins, DNA and RNA and it exhibits a repeating structure (van Holde, 1988). The basal unit of chromatin, the nucleosome, is composed of a histone octamer (two each of H2A, H2B, H3 and H4) around which two superhelical turns of DNA are wrapped (van Holde, 1988). The structure of both the histone octamer (Arents et al, 1991)... 

More recent studies in Drosophila revealed that H3.3 also plays an important role in the male pronucleus after fertilization (Loppin et al. 2005). The loss of the H3.3 chaperone HIRA impairs the replacement of paternal non-histone proteins from the sperm nucleus with maternally provided histones including H3.3, while the maternal genome exclusively contains the canonical H3. Thus, H3.3 and its deposition factor HIRA function in early fertilization events and might have a role in imprinting in higher eukaryotes. 

Olson MO, Ezrailson EG, Guetzow K, Busch H (1975) Localization and phosphorylation of nuclear, nucleolar and extranucleolar non-histone proteins of Novikoff hepatoma ascites cells. J Mol Biol 97 611-619... 

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