Figure 3.

Tat-SF1 directly and preferentially associates with the ULM region of SF3b1. GST-pulldowns of purified recombinant proteins were resolved by SDS-PAGE and stained with Coomassie® Brilliant Blue. Three lanes were loaded for each experiment: I, input (1 μg); W, final wash of bound resin; E, elution. The sizes of molecular weight standards (STD) and subunits are indicated. GST is a control for nonspecific binding. A, GST-fused Tat-SF1 (residues 1–360) retains the SF3b1 ULM region (“SF3b1^ULM”, residues 190–344) and B, shows little retention of UHMK1-phosphorylated (P) SF1. Likewise, C, GST-U2AF⁶⁵ΔRS (residues 85–475) shows little Tat-SF1 retention, whereas GST-SF3b1^ULM significantly retains Tat-SF1.