Histones structure plate

Figure 1. Hierarchical model of chromosome structure, (a) In interphase cells, DNA is packed in a nucleus as forming nucleosome and chromatin, (b) DNA forms nucleosome structure together with core histone octamer, which is then folded up into 30nm fiber with a help of linker histone HI. This 30 nm fiber is further folded into 80 nm fiber and 300 nm loop structures in a nucleus. In mitosis, chromosome is highly condensed. Proteins which are involved in each folding step are indicated above and non-protein factors are indicated below, (c) The amino acid sequences of histone tails (H2A, H2B, H3 and H4) are shown to indicate acetylation, methylation and phosphorylation sites. (See Colour Plate 1.)...

Figure 2. Effect of H2A.Bbd on transcription. The presence of H2A.Bbd confers lower stability and more loose structure to the nucleosomes, which allows the transcription factors binding to this variant nucleosome and thereby recruitment of p300 and acetylation of the promoter proximal histones. The remodeling complex can not mobilize the variant nucleosome, but instead helps in the removal of H2A.Bbd-H2B dimer. All these events facilitate transcription. (See Colour Plate 9.)...

Figure 1. Different histone chaperones in the key histone metabolic pathways Functions of histone chaperones range from the storage of newly synthesized histones in the cytoplasm, its transfer into the nucleus and in histone assembly into nucleosomes. Apart from diis die histone chaperones are also involved in histone exchange, maintenance of heterochromatin and in the regulation of chromatin structure during transcription. (See Colour Plate 10.)...

Plate 12. Mechanistic effect of acetylation/deacetylation of histones and nonhistones on chromatin structure.(a) Acetylation of non-histone proteins results in transcriptional activation (b) Acetylation of ORCl by HBOl is important for replication, (c) Acetylation of newly synthesized histones necessary for chromatin assembly. (See Chapter 9 Figure , p. 195.)... 

Plate 22 Core particle of the nucleosome. The 146 bp DMA superhelix is on the outside and the eight histone protein chains are in blue and on the inside. The view is down the DNA superhelix. The structure shows in atomic detail how the histone protein octamer is assembled and how 146 base pairs of DNA are organized into a superhelix around it. Histone amino-terminal tails pass over and between the gyres of the DNA superhelix to contact neighbouring particles. The lack of uniformity between multiple histone-DNA-bInding sites causes the DNA to deviate from ideal superhelix geometry. (Reproduced with permission of the authors and Nature from ref. 33 of Chapter 9 see also ref. 34 of Chapter 9 for comments.)... 

Figure 4.15, Crystal structure of the nucleosome, downloaded from the Protein Data Bank (ID lAOI) and visualized in ribbon format in Rasmol [117]. (Top) Front view. (Bottom) Side view. The eight histone proteins are in greens and blues, and DNA double helix, wrapped around the histone core 1.5 times, is in orange-red and gold. (See color plates).

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