Methyltransferase substrates are useful for the assay of various histone methyltransferases either by radiolabeling with [3H]-S-adenosylmethionine (e.g. gel electrophoresis/autoradiography or filterplate/scintillation counting) or by methods employing site/modification-specific antibodies (e.g. anti-H3K4me2). Reaction Biology offers several methyltransferase substrates for purchase.