Strengthening the PY tract eliminates the role of the C-rich motifs. (a) LCAT intron 4 with the mutations shown in blue above the WT sequence. BPS, branchpoint. (b) Splicing of the LCAT intron 4 mini-genes (WT, MUT6, MUT24, MUT24, MUT17, MUT20, MUT48, MUT49 and MUT 16B) in HeLa cells. Analysis was performed as in Figure 4. (c) Graphical representation of the percent pre-mRNA for each LCAT mini-gene. Error bars represent standard deviation of replicate experiments.