Protein N-arginine methylation in subcellular fractions of lymphoblastoid cells

Arginine methylation in RNA-binding proteins containing arginin- and glycin e-rich RGG motifs is catalyzed by specific protein arginine N-methyltransfe rase in cells. We previously showed that lymphoblastoid cells grown in the presence of an indirect methyltransferase inhibitor, adenosine dialdehyde ( AdOx), accumulated high level of hypomethylated protein, substrates for the endogenous protein methyltransferases or recombinant yeast arginine methyl transferase [Li, C, et at (1998) Arch. Biochem. Biophys, 351, 53-59], In th is study we fractionated the lymphoblastoid cells to locate the methyltrans ferases and the substrates in cells. Different sets of hypomethylated methy l-accepting polypeptides with wide range of molecular masses were present i n cytosolic, ribosomal, and nucleus fractions. The methylated amino acid re sidues of the methyl-accepting proteins in these fractions were determined. In all three fractions, dimethylarginine was the most abundant methylated amino acid. The protein-arginine methyltransferase activities in the three fractions were analyzed using recombinant fibrillarin (a nucleolar RGG prot ein) as the methyl-accepting substrate. Fibrillarin methylation was stronge st in the presence of the cytosolic fraction, followed by the ribosomal and then, the nucleus fractions. The results demonstrated that protein-arginin e methyltransferases as well as their methyl-accepting substrates were wide ly distributed in different subcellular fractions of lymphoblastoid cells.