PEPTIDES WITH SEQUENCES SIMILAR TO GLYCINE, ARGININE-RICH MOTIFS IN PROTEINS INTERACTING WITH RNA ARE EFFICIENTLY RECOGNIZED BY METHYLTRANSFERASE(S) MODIFYING ARGININE IN NUMEROUS PROTEINS

Several proteins that interact with RNA, e.g. the heterogenous ribonuc leoprotein particle A and B proteins, fibrillarin and nucleolin, conta in the modified amino acid N(G),N(G)-dimethylarginine. Here, we report that two synthetic peptides, Ac-GGRGGFGGRGGFGGRGGFG-NH2 (R3) and GGFG GRGGFG-NH2 (R1), which are based on methylated sequences in fibrillari n and nucleolin, inhibit the methylation of a large majority of the me thyl-accepting proteins observed in extracts of adenosine dialdehyde-t reated PC12 cells. Concomitantly, the peptides themselves become methy lated, suggesting that they compete for the same enzyme that carries o ut the bulk of N-methylation in PC12 cells. R3 potently inhibits forma tion of N(G),N(G)-dimethylarginine in PC12 substrates, with a lesser e ffect on N(G)-monomethylarginine and N(G),N'(G)-dimethylarginine. Bovi ne brain contains an activity that methylates PC12 methyl acceptors. A fter partial purification, the bovine methyltransferase efficiently mo difies R3 and R1, yielding half-maximal rates of methylation at approx imately 0.2 and approximately 2 muM peptide, respectively. A search of the GenPept database for the FGGRGGF motif revealed 13 candidate meth yl acceptors containing arginine and at most two similar substitutions or one mismatch. Of these, 10 are known or presumed to interact with RNA. These findings are consistent with the hypothesis that a majority of proteins containing N(G),N(G)-dimethylarginine interact with RNA.