DELTA-N-METHYLARGININE IS A NOVEL POSTTRANSLATIONAL MODIFICATION OF ARGININE RESIDUES IN YEAST PROTEINS

We have found a novel modification of protein arginine residues in the yeast Saccharomyces cerevisiae, Intact yeast cells lacking RIMT1, the gene encoding the protein omega N-G-arginine methyltransferase, were labeled with the methyl donor S-adenosyl-L-[methyl-H-3]methionine, The protein fraction was acid-hydrolyzed to free amino acids, which were then fractionated on a high resolution sulfonated polystyrene cation e xchange column at pH 5.27 and 55 degrees C, In the absence of the omeg a-N-G,(NL)-L-G-[H-3]dimethylarginine product of the RIMT1 methyltransf erase, we were able to detect a previously obscured H-3-methylated spe cies that migrated in the region of methylated arginine derivatives. T he [H-3]methyl group(s) of this unknown species were not volatilized b y treatment with 2 M NaOH at 55 degrees C for up to 48 h, suggesting t hat they were not modifications of the terminal omega-guanidino nitrog en atoms. However, this base treatment did result in the formation of a new H-3 methylated derivative that co-chromatographed with delta-N-m ethylornithhine on high resolution cation exchange chromatography, on reverse phase high pressure liquid chroma tography, and on thin layer chromatography, From these data, we suggest that the identity of the o riginal unknown methylated residue is delta-N-monomethylarginine. The presence of this methylated residue in yeast cells defines a novel typ e of protein modification reaction in eukaryotes.