Higher-order chromatin

Histone tails are the N-terminal regions of histones which reach outside the nucleosomes. They are not essential for the formation in of nucleosomes but are required for the formation of higher-order chromatin structures. The histone tails are also known to be heavily posttranslationally modified by acetylation, phosphorylation, methylation, etc. and are important for the regulation of gene activity. 

Varga-Weisz PD, Becker PB (2006) Regulation of higher-order chromatin structures by nucleosome-remodelling factors. Curr Opin Genet Dev 16 151-156... 

Mirkovitch J, Mirault ME, Laemmli UK (1984) Organization of the higher-order chromatin loop Specific DNA attachment sites on nuclear scaffold. Cell 39(l) 223-232 Mitchell RS, Beitzel BF, Schroder AR, Shinn P, Chen H, Berry CC, Ecker JR, Bushman FD (2004) Retroviral DNA integration ASLV, HIV, and MLV show distinct target site preferences. PLoS Biol 2(8) E234... 

Crystal packing features of NCP and implications for higher order chromatin structure... 

Fig. 20. Packing interactions between NCP molecules, which are a consequence of crystallization, nevertheless provide hints for higher order chromatin structure assembly, (a) Histone-histone interactions shown at the site of the cacodylate ion. In addition to binding interactions with the cacodylate ion, the N-terminal tail is involved in significant interactions with the patch of acidic residues on the dimer face of the neighbor NCP. The orientation of the dyad alternates between the two NCP molecules, (b) DNA base stacking is continuous between neighboring NCP molecules in the crystal lattice as the DNA exits one NCP and enters the next. The stacking interaction is strong enough to force a shift in the terminal phosphates for adjoining 5 termini.

Carruthers, L.M., Bednar, J., Woodcock, C.L., and Hansen, J.C. (1998) Linker histones stabilize the intrinsic salt-dependent folding of nucleosomal arrays mechanistic ramifications for higher-order chromatin folding. Biochemistry 37, 14776-14787. 

Schwarz, P.M. and Hansen, J.C. (1994) Formation and stability of higher order chromatin structures-contributions of the histone octamer. J. Biol. Chem. 269, 16284-16289. 

Linker histones and higher order chromatin structures... 

Daban, J.R. (2000) Physical constraints in the condensation of eukaryotic chromosomes. Local concentration of DNA versus linear packing ratio in higher order chromatin structures. Biochemistry 39, 3861-3866. 

The ISWI chromatin-remodeling protein is required for gene expression and the maintenance of higher order chromatin structure in vivo. Mol. Cell 5, 355-365. 

P.R. (1990) Periodicity of DNA folding in higher order chromatin structures. EMBO J. 9, 1319-1327. 

Figure 31.18. Higher-Order Chromatin Structure. A proposed model for chromatin arranged in a helical array consisting of six nucleosomes per turn of helix. The DNA double helix (shown in red) is wound around each histone octamer (shown in blue). [After J. T. Finch and A. Klug. Proc. Natl. Acad. Sci. USA 73(1976) 1900.]...

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