C-rich motifs function as ISEs in GNPTG intron 2. (a) GNPTG intron 2 with the mutations shown in blue above the WT sequence and the putative branchpoint sequence shown in bold. (b) Splicing of the GNPTG intron 2 mini-genes (WT and MUT) in HeLa cells. Splicing products (isolated from HeLa, reverse-transcribed and amplified with radioactive PCR) were resolved on a 10% non-denaturing gel and scanned using a phosphorimager. The average quantification and standard deviation of the percent pre-mRNA (pre-mRNA divided by total RNA) for triplicate reactions is reported below each lane. (c) Graphical representation of the percent pre-mRNA for the WT and MUT GNPTG mini-genes. Error bars represent standard deviation of replicate experiments.