RESULTS AND DISCUSSION CD28-induced an increase of R-methylation and protein arginine methyltransferase activity

To test whether T cell activation induced R-methylation of cellular proteins we used an antimethyl-R antibody (-Dma).-Dma reacted in immunoblot (Fig. 1 A, left) and immunoprecipitation (Fig. 1 A, middle) with an Arg-Gly-Gly (RGG)-containing sequence (P3) of Sam68 (8) after in vitro methylation by glutathione S-transferase (GST)-PRMT1, assessed by radioactive labeling (Fig. 1 A, right).-Dma recognized a few proteins in unstimulated primary T cells by immunoblotting (Fig. 1 B). Their detection increased at 5 min after superantigen (sAg) and B7 costimulation, gradually rising up to 30 min and several other proteins (20–120 kD) became visible only after 10–30 min.-DMA reactivity decreased toward pro-