Characterization of the Activity and Biological Function of Human Protein Arginine Methyltransferase 9 (PRMT9)

Abstract

Protein arginine methyltransferases (PRMTs) make up a family of enzymes that transfer methyl groups onto arginine residues and play important roles in DNA repair, splicing, transcriptional control and signaling. In mammals, a family of nine PRMTs are known. PRMT1,2,3,4,6, and 8 catalyze the formation of asymmetric dimethylarginine (ADMA) and w‐monomethylarginine (MMA), PRMT5 catalyzes symmetric dimethylarginine (SDMA) and MMA formation, and PRMT7 catalyzes only MMA formation. The last member of this family, PRMT9 (also designated PRMT10), has not previously been characterized. In humans, it is encoded on a gene on chromosome 4 in position 4q31. We have now expressed human PRMT9 both as a GST‐fusion protein in bacterial cells and as a GFP‐fusion protein in human HEK293 cells. For both expression systems, we have also prepared catalytic mutants to serve as controls for possible contamination of other types of PRMTs. Using an in vitro methylation assay, we show that both forms of PRMT9 catalyze the methylation of myelin basic protein and a GST‐fusion protein of the N‐terminal domain of human fibrillarin. Studies are in progress to characterize the type of activity and physiological substrates for PRMT9.