(A) Schematic representation of the insulin expression construct containing 2 introns and the respective flanking exons I1, I2 and I3. SV40 promoter/enhancer regions and insulin transcription terminators are shown in black. Primers used for PCR are indicated. (B) HeLa cells were transfected with increasing concentrations (0, 0.25, 0.3, 0.35, 0.5 and 0.7 μg) of plasmids expressing wild-type and mutant SRPK1 along with 1.65 μg of the reporter gene. Cells were treated with 50 μg/ml 5-FU for 24 h, prior harvesting. RNA was isolated 48 h following transfection, and RT-PCR was carried out. The spliced and unspliced products have a size of 0.3 and 1 kb respectively. (C) The ratio of the upper and lower bands was quantified using ImageJ software. Data represent the means ± SE of two independent experiments. (D) Western blots showing the levels of wild-type and mutated SRPK1.