G-rich motifs function as ISEs in LCAT intron 4 splicing. (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, MUT3, MUT4, MUT7 and MUT 5) in HeLa cells. Splicing products (isolated from HeLa, reverse-transcribed and amplified with radioactive PCR) were resolved on an 8% non-denaturing gel and scanned using a phosphorimager. The pre-mRNA (top) is a 472 bp product and the mRNA (bottom) is a 389 bp product. The average quantification and standard deviation of the percent pre-mRNA (pre-mRNA divided by total RNA) for at least triplicate reactions is reported below each lane. (c) Graphical representation of the percent pre-mRNA for each LCAT mini-gene. Error bars represent standard deviation of replicate experiments.