1. Which of the four histones has the largest tail? Do histone tails play an imp
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Question
1. Which of the four histones has the largest tail? Do histone tails play an important role in the organization of core nucleosome particle? How do histone tail modifications contribute to chromatin structure?
2. Speculate all the different kinds of interaction of histones with DNA in the nucleosome that may contribute to its structural stability. Where on the nucleosome do you think this interaction maybe the weakest? In this context also discuss what is meant by the “histone fold”?
4. What holds the tetramer (the two H3/H4 dimers) together in the core nucleosome structure? Which dimer (H3/H4 or H2A/H2B) interacts near a) the dyad axis and b) the entry exit site? What promotes the interaction of the H2A/H2B dimer with the tetramer?
Explanation / Answer
1.
H3 N- terminal tail is the longest.
Yes, histone tails play important role in the organization of core nucleosome particle. They stabilizes DNA wrapping around the octamer. The charged N-terminal histone tails stabilize the 30 nm fibers by interacting with adjacent nucleosomes. Modification of the N-terminal tails of the histones alters cromatin accessibility and hence regulates the transcription and expression of genes.
Histone tail modifications include acetylation/methylation of lysine residues, methylation of arginine residues, phosphorylation of serine and threonine residues. Acetylation and phosphorylation reduce the positive charges of the histone tails resulting in loss of interaction with negatively charged sugar-phosphate backbone of DNA.
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