Post-synthetic modifications of nuclear proteins. High mobility group proteins are methylated.

Calf thymus high mobility group proteins 1 and 2 (HMG-1 and HMG-2) were purified to homogeneity from a 0.35 M NaCl extract of chromatin by selective precipitation with trichloroacetic acid followed by ion exchange chromatography on CM-Sephadex. Amino acid analysis of an acid hydrolyzate of HMG-1 and HMG-2 proteins revealed the presence of a ninhydrin-positive peak identified as N^G,N^G-dimethylarginine. Radioactive tracer experiments confirmed the presence of methylated arginine in HMG proteins.