c 2 =0.258

1. c2=0.258 c2=0.808 c2=6.80 c2=11.3 c2=1.42 c2=2.77 c2=0.413 c2=0.337 c2=0.993 c2=1.31 c2=0.991 c2=1.6 c2=0.997 c2=3.79 c2=1.26 Supplementary Figure 1. Residual plots and corresponding c2 values for the fit of models to the SPR data presented in Figures 1, 2 and 3 of the main text. The combined residuals from the fit to the series of sensorgrams are shown. Starting from the top row (left to right), Figure 1A HuR12, HuR123, TIAR12; Second row, Figure 1A TIAR123, Figure 1B HuR12, HuR123; Third row, Figure 1B TIAR12, TIAR123, Figure2 HuR12-8mer; Fourth row, Figure 2 HuR12-13mer and HuR12-17mer, Figure 3A HuR12; Bottom row, Figure 3A TIAR12, Figure 3B HuR12 and TIAR12.

2. A B C Supplementary Figure 2. Size exclusion chromatography profiles (SuperdexTM 200 5/150 GL column from GE Healthcare) showing the interaction of TIAR12 and the 13-nt U-rich RNA used in the SAXS studies. A) 13U RNA alone, B) equimolar TIAR12 alone (shown on the same absorbance scale, its absorption at both wavelengths is much lower than that of the RNA) and C)13U-rich RNA and TIAR12 combined. The early eluting peak (indicated by the arrow) represents the TIAR12/RNA complex, followed by dissociated RNA.