In vitro radioactive methylation assay

Recombinant proteins were incubated with 17.3 μM S-adenosyl-l-[methyl-¹⁴C]methionine (PerkinElmer) and enzyme in methylation buffer [50 mM tris-HCl (pH 8.0), 20 mM KCl, 5 mM MgCl₂, 2 mM DTT, 10% glycerol] at 30°C for 2 hours. The samples were run on SDS-PAGE, dried, and exposed to a phosphor screen for 3 days.