Splice site strength modulates RNA pairing-mediated alternative exon 4 selection. (A) Splice sites built on exon clusters in Drosophila srp genes. The 5′ and 3′ splice site motif scores were calculated using the splice site predictor (Reese et al. 1997) (range is 0–1, with higher values predicting stronger splice sites). Statistical analysis revealed that the splice site of exon 4.2 is significantly stronger than that of exon 4.1. (***) P < 0.001 (Student's t-test, two-tailed). Symbols used are the same as those in Figure 1. (B) Splice site sequences of the wild-type and mutants, with the scores on the right. Uppercase letters indicate exon sequences; lowercase letters indicate intron sequences. Mutated nucleotides are marked in red. (C) Effect of strengthening the weak splice sites on alternative exon 4.1 inclusion. (D) Comparison of the effect of strengthening the weak splice sites on alternative exon 4.1 inclusion in the presence versus disruption of downstream RNA pairing. (E) Effect of changing the splice sites on alternative exon 4.2 inclusion. (F) Comparison of the effect of changing the splice sites on alternative exon 4.2 inclusion in the presence versus disruption of upstream RNA pairing. Data are expressed as percentages of the mean ± SD from three independent experiments.
