Methylation of the arginine in the RGG domain of Sbp1 was done essentially as previously described (Hsieh et al. 2007) with the following modifications. Briefly, plasmids containing Sbp1 and type I arginine methyltransferase Hmt1 were cotransformed and coexpressed in E. coli BL21 (DE3) cells. Methylated Sbp1 was purified by affinity chromatography followed by ion-exchange chromatography using HiTrap Heparin HP column (GE Healthcare). Methylation of the arginines in the RGG domain was confirmed by LC–MS/MS.