Fig. 4. SRSF1 RRM1 interacts with RNA on both sides of RRM2-binding site.

A Schematic representation of the RNA molecules used for the SELEX experiment. Invariant GGA nucleotides were inserted in the middle of the degenerated sequence to recruit SRSF1 RRM2 and allow the selection of potential RRM1 binding sites on both sides of the motif. B The sequences selected by SELEX with SRSF1 RRM12 followed two main patterns containing either the GGA or a GGANGGA motif. To determine the positions with the most stringent selection during SELEX, we calculated the relative entropy of position-dependent nucleotide frequency distributions of foreground and background sequences (lower panels). C Overlay of ¹H-¹⁵N HSQC spectra measured with SRSF1 RRM1+2 YS free form and in the presence of UCAUUGGAU or UGGAUUUUUCAU RNA at 0.3:1 and 1:1 RNA:protein ratios (in blue, orange, and red, respectively). D Mapping of the chemical-shift perturbations observed upon interaction of SRSF1 RRM1+2 YS with the two RNAs tested in C. SRSF1 RRM1 binds equally well the cytosine located at −4 or +6 from the GGA motif.