Alternative splicing yields protein arginine methyltransferase 1 isoforms with distinct activity, substrate specificity, and subcellular localization

PRMT1 is the predominant member of a family of protein arginine methyltransferases (PRMTs) that have been implicated in various cellular processes, including transcription, RNA processing, and signal transduction. It was previously reported that the human PRMT1 pre-mRNA was alternatively spliced to yield three isoforms with distinct N-terminal sequences. Close inspection of the genomic organization in the 5'-end of the PRMT1 gene revealed that it can produce up to seven protein isoforms, all varying in their N-terminal domain. A detailed biochemical characterization of these variants revealed that unique N-terminal sequences can influence catalytic activity as well as substrate specificity. In addition, our results uncovered the presence of a functional nuclear export sequence in PRMT1v2. Finally, we find that the relative balance of PRMT1 isoforms is altered in breast cancer.