[bu.edu](https://www.bu.edu/prelaw/preparing-for-law-school/exploring-the-law-profession/)PR-Set7 is a nucleosome-specific methyltransferase that modifies lysine 20 of histone H4 and is related to silent chromatin. Lysine for cats is much like Vitamin C for people. YEA My 5 yr old daughter came down with a horribly severe case of canker sores.