Figure 1.

PRMT5 is dimethylated at Arg-505. A, SimplyBlue SafeStain of an SDS-PAGE gel of FLAG antibody immunoprecipitates from Lys-562 cells stably overexpressing PRMT5-FLAG before analysis by MS. Protein bands corresponding to PRMT5 and LYAR (with peptide sequences: KKGQEADLEAGGEEVPEANGSAGKR; VHNESILDQVWNIFSEASNSEPVNKEQDQRPLHPVANPHAEISTK) are indicated. B, ESI MS/MS spectrum of the tryptic peptide EKDRDPEAQFEmPYVVR^## (where m is oxidized methionine and R^## represents dimethylated arginine). All y ions in the dimethylated peptide spectrum have a mass shift of +28 Da compared with the y ions from the nonmethylated peptide spectrum. C, amino acid sequence alignment of PRMT5 proteins among mammals. The Homo sapiens PRMT5 amino acid sequence from residues 486 to 530 is indicated on the top, and the conserved arginine (Arg-505 in Homo sapiens) is indicated by an asterisk.