Histone H3 (21-44), derived from histone H3 21-44 amino acids, is usually used as a substrate (such as protein arginine methyltransferases) for methylation assays[1].
References
[1] Santos-Rosa H, Caldas C. Chromatin modifier enzymes, the histone code and cancer. Eur J Cancer. 2005;41(16):2381-2402. DOI:10.1016/j.ejca.2005.08.010
