A sensitive assay for histone methyltransferase.

Abstract A method is described for the assay of histone methyltransferase using soluble histones as substrate. The precipitation of the methylated protein on chromatography paper allows for greater sensitivity and more rapid sample processing than have previously been reported. After incubation of the enzyme in the presence of radioisotopically labeled S -adenosyl- l -methionine and soluble rat brain histone, the residual S -adenosyl- l -methionine is removed by extensive washing in 1.1 m trichloroacetic acid. The amount of methyl groups incorporated into histones is measured by liquid seintillation counting. This procedure can probably be used to assay other protein methylases. A comparison is made between this assay and one using chromosomal bound histones as substrates.