Protein arginine methyltransferase I: substrate specificity and role in hnRNP assembly.

Prmt1, the major protein arginine methyltransferase in mammalian cells, has been implicated in signal transduction, transcriptional control, and protein trafficking. In the present study, mouse embryonic stem cells homozygous for an essentially null mutation in the Prmt1 gene were used to examine Prmt1 activity and substrate specificity, which by several criteria appeared to be highly specific. First, other methyltransferases did not substitute for the loss of Prmt1 activity.