Methylation at the guanidino group in the arginine side chain, a eukaryotic-specific modification, has been suggested as one of the most extensive protein methylations in mammalian cells (Najbauer et al. 1993; McBride and Silver 2001; Pahlich et al. 2006; Bedford and Clarke 2009; Blanc and Richard 2017). This modification plays important physiological roles from DNA repair, transcriptional regulation, mRNA splicing, to protein translocation and signal transduction. Sbp1 is a known target for the arginine methyltransferase (Hmt1) (Frankel and Clarke 1999), but the physiological function of this modification remains unknown.