Fig. 3.

U1-70K binding by SRSF1. (A) Schematic representation of domain maps and fragments of U1-70K (left), phosphorylation mimetic versions of SRSF1 (right), and sequences and phosphorylated sites of RS1 and RS2 domains (bottom). (B) GST pull-down assay between different GST-SRSF1 constructs (10 μg) and 5 μl of in vitro transcribed-translated [³⁵S]-met labeled U1-70K constructs in the presence of RNase A (upper) or in the presence of cognate RNAs, Ron ESE and U1 snRNA (bottom). (C) Models depicting intra- and intermolecular binding modes within and between SRSF1 and U1-70K. (D) In vitro splicing of β-gb pre-mRNA in S100 complementation assay using WT and different phosphorylation mimics of SRSF1 (FL). Relative splicing efficiency of SRSF1 phosphomimetic mutants is shown in the bottom of the gel.