<p style="margin-left: 40px">&nbsp;Histone modification is modification to the histone proteins. Because role of histone protein is packing of DNA, modification of it alters gene expression by regulating packing. At tightly packed DNA, transcription factor can&rsquo;t easily bind to the DNA, so gene expression is down regulated. Modification includes methylation, phosphorylation, acetylation, ubiquitiylation, and sumoylation. It usually happens in the tail protruding from the histone core of the nucleosome, and also this modification site exits within the globular histone core. In the class, we think about why histone tail exists. I think that enzyme like DNMT1 can easily bind to the histone tail than histone core because histone tail is more accessible than histone core. I guess that that&rsquo;s why the modification of histone tail is more common than modification of histone core.</p>

<p style="margin-left: 40px">&nbsp; There are many technologies for studying epigenomics. In the class I learned about bisulfate sequencing. When bisulfate is treated to the DNA, cytosine residues are converted to uracil, but 5-methylcytosine residues is not affected. By sequencing, we can know the methylated and unmethylated cytosine.</p>

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