Mutant Ataxin-1 reduces histone acetylation resulting in repressed histone acetyltransferase-mediated transcription. Histones undergo acetylation on their lysine residues by enzymes known as histone acetyltransferase. This occurs through polycomb mediated gene silencing via histone methylation and chromodomain interactions. This allows it to regulate global chromatin structure via histone acetylation. Bromodeoxyuridine releases gene silenced by association with the histone caused by DNA methylation. PAD4 regulates gene expression through histone modifications. The biological consequences of histone methylation are context dependent. Methylation, along with histone modification, is central to imprinting. A second major role of lysine is in epigenetic regulation by means of histone modification. These HATs are known to acetylate all of the histone subunits in the nucleosome. Ramakrishnan is also known for his past work on histone and chromatin structure. Chemical modifications of histone proteins often occur on particular amino acids. Its action is opposite to that of histone acetyltransferase. In budding yeast, the candidate gene for activation of histone gene expression is SBF. This protein is a specialized isoform of histone H3.