Journal of Undergraduate Research


histone code, post-translational modifications, nucleosome positioning


Life Sciences


Microbiology and Molecular Biology


Nucleosomes are the fundamental unit of chromatin organization. They consist of an octamer of histone proteins (two of each H2A, H2B, H3, and H4) wrapped around by 147 base pairs of DNA. Their positioning and occupancy around important genetic elements such as enhancers and promoters are some of the most important means of epigenetic regulation: changes in expression of genes that reflect a change in something other than DNA sequence. For example, highly-expressed genes are generally associated with low nucleosome occupancy, whereas inactive genes are associated with high nucleosome occupancy. It has also been shown that the positioning of nucleosomes is well-regulated around promoters and enhancers. In addition, different post-transcriptional modifications (PTMs) to amino acid residues on histone tails are correlated with different chromatin states. Among the most well-characterized PTMs are acetylation to lysine residues on the histone protein H3. The precise mechanisms of how PTMs regulate chromatin states are still under investigation.

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