Fig 1: In vitro substrates of the major enzymes PRMT1, PRMT4/CARM1, and PRMT5(A) Oriented peptide array library (OPAL) substrate degeneracy schematic. As shown, the substrate arginine (R) is fixed as is one other position per mixture (Z) (locations −3,-2,-1, or 1,2,3 relative to the fixed R). The remainder of the substrate peptide residues are degenerate (X).(B) Homo sapiens (Hs) PRMT1 relative activity toward the OPAL substrate library. Each row represents the fixed amino acid in each position. Charged residues are colored (blue = positive, red = negative) and shown at the top. Relative activity is shown as a heatmap (0–100%, white to blue).(C) HsPRMT4/CARM1 relative activity shown as a heatmap.(D) C. elegans (Ce) PRMT5 relative activity shown as a heatmap.(E) X. laevis (Xl) PRMT5-MEP50 complex relative activity shown as a heatmap.(F) Sequence logo probability plot of PRMT1 relative activity. Acidic residues are shown in red, basic in blue, hydrophobic in black, neutral in purple, and polar residues shown in green.(G) Sequence logo probability plot of HsPRMT4/CARM1 relative activity.(H) Sequence logo probability plot of CePRMT5 relative activity.(I) Sequence logo probability plot of XlPRMT5-MEP50 relative activity.