Nucleosome histone interactions

Hyde and Walker, 1975a) indicate that there are two basic types of histone-histone interactions or contacts those within the nucleosome which result in the formation of histone octamers and those between nucleosomes which give rise to higher oligomers. 

This may be correlated with the conservation of the primary sequences of the carboxy-terminal regions of the histones and the indications that these are the sites of histone-histone interaction within the nucleosomes (Spiker and Isenberg, 1978). 

B. DNA-Core Histone Interactions Involved in Formation of the Nucleosome... 

It is not widely appreciated that the major aspects of core histone interactions were well understood even before the development of the nucleosome model. Evidence for strong H2A H2B dimer interactions and an FI3 H4 tetramer was available in the early seventies (see Ref. [1], Chapter 2). By 1978, the rigorous sedimentation equilibrium studies from Moudrianakis laboratory had elucidated the thermodynamics of octamer formation [7]. What was missing, of course, was any structural information concerning these interactions. This was overcome by arduous X-ray diffraction studies, culminating in the elegantly detailed structures we have today [15,17,18], see also Flarp et al., this volume, p. 13. We now know how the core... 

Histones within transcriptionally active chromatin and heterochromatin also differ in their patterns of covalent modification. The core histones of nucleosome particles (H2A, H2B, H3, H4 see Fig. 24-27) are modified by irreversible methylation of Lys residues, phosphorylation of Ser or Thr residues, acetylation (see below), or attachment of ubiquitin (see Fig. 27-41). Each of the core histones has two distinct structural domains. A central domain is involved in histone-histone interaction and the wrapping of DNA around the nucleosome. A second, lysine-rich amino-terminal domain is generally positioned near the exterior of the assembled nucleosome particle the covalent modifications occur at specific residues concentrated in this amino-terminal domain. The patterns of modification have led some researchers to propose the existence of a histone code, in which modification patterns are recognized by enzymes that alter the structure of chromatin. Modifications associated with transcriptional activation would be recognized by enzymes that make the chromatin more accessible to the transcription machinery. 

Where chromatin is being activated for transcription, the nucleosomal histones are further acetylated by nuclear (type A) HATs. The acetylation of multiple Lys residues in the amino-terminal domains of histones H3 and H4 can reduce the affinity of the entire nucleosome for DNA. Acetylation may also prevent or promote interactions with other proteins involved in transcription or its regulation. When transcription of a gene is no... 

Ettig R, Kepper N, Stehr R et al (2011) Dissecting DNA-histone interactions in the nucleosome by molecular dynamics simulations of DNA unwrapping. Biophys J 101(8) 1999-2008... 

Each of the histone proteins making up the nucleosome core contains a flexible amino terminus of 11-37 residues extending from the fixed structure of the nucleosome these termini are called histone tails. Each H2A also contains a flexible C-termlnal tall (see Figure 10-20b). The histone tails are required for chromatin to condense from the beads-on-a-string conformation Into the 30-nm fiber. Several positively charged lysine side chains In the histone tails may interact with linker DNA, and the tails of one nucleosome likely interact with neighboring nucleosomes. The histone tail lysines, especially those In H3 and H4, undergo reversible acetylation and deacetylation by enzymes that act on specific lysines In the N-termlnl. In the acetylated form, the positive... 

The term M.c. was first coined by R. A.Laskey et al. [Nature 275 (1978) 416-420] to describe the action of nucleoplasmin, an acidic nuclear protein that mediates the in vitro assembly of nucleosomes from histones and DNA. In solutions of physiological ionic strength in vitro, DNA and histones interact to form a precipitate. If the histones are first mixed with a molar excess of nucleoplasmin, the positive charges of the histones are decreased by the nucleoplasmin subsequent addition of DNA results in the formation of soluble nucleosome cores and release of the nucleoplasmin. Further development of the M.c. concept was initiated by the work of R.J. Ellis on ribulose huphosphate carboxylase-oxygenase (rubisco). It has been suggested that prions may be rogue M.c. [R. J. Ellis S.M. van der Vies Arum. Rev. Biochem. 60 (1991) 321-347 R.J.Ellis etal. (eds.) Phil Trans. Roy. Soc. Land. B 338 (1993) 255-373 D.Wall etal. J.Biol. Chem. 270 (1995) 2139-2144 J.S.Weissman et al. Cell 84 (1996) 481 90 A. A. Antson et al Circular Assemblies Curr. Opin. Struct. Biol. 6 (1996) 142-150 P. A. Cole Chaperone-assisted protein expression Structure 4 (1996) 239-242]... 

Histones are small, basic proteins required to condense DNA into chromatin. They have been first described and named in 1884 by Albrecht Kossel. There are five main histones HI, H2A, H2B, H3 andH4. An octamer of core histones H2A, H2B, H3 andH4 is located inside a nucleosome, the central building block of chromatin, with about 150 base pairs of DNA wrapped around. The basic nature of histones, mediated by the high content of lysine and arginine residues, allows a direct interaction with the acidic phosphate back bone of DNA. The fifth histone HI is located outside at the junction between nucleosomes and is referred to as the linker histone. Besides the main histones, so-called histone variants are known, which replace core histones in certain locations like centromers. 

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