The mammalian immediate-early TIS21 protein and the leukemia-associated BTG1 protein interact with a protein-arginine N-methyltransferase.

The TIS21 immediate-early gene and leukemia-associated BTG1 gene encode proteins with similar sequences. Two-hybrid analysis identified a protein that interacts with TIS21 and BTG1. Sequence motifs associated with S-adenosyl-L-methionine binding suggested this protein might have methyltransferase activity. A glutathione S-transferase (GST) fusion of the putative methyltransferase modifies arginine residues, in appropriate protein substrates, to form NG-monomethyl and NG,NG-dimethylarginine (asymmetric). We term the protein- arginine N-methyltransferase (EC 2.1.1.23) gene "PRMT1, " for protein-arginine methyltransferase 1. GST-TIS21 and GST-BTG1 fusion proteins qualitatively and quantitatively modulate endogenous PRMT1 activity, using control and hypomethylated RAT1 cell extracts as methyl-accepting substrates. PRMT1 message appears ubiquitous, and is constitutive in mitogen-stimulated cells. Modulation of PRMT1 activity by transiently expressed regulatory subunits may be an additional mode of signal transduction following ligand stimulation.