Analysis of hERG1 intron 9 poly(A) signal. A, diagram of the tandem poly(A) signal construct including the SV40 promoter, firefly luciferase gene, hERG1 intron 9 poly(A) signal, and the synthetic poly(A) signal. The RPA probe and RNase-protected fragments corresponding to RNA terminated at the intron 9 poly(A) and the synthetic poly(A) sites are indicated. B, RPA analysis of wild-type (WT), mutant (Mut), and canonical (Can) hERG1 intron 9 poly(A) signals. Unt, untransfected control. Quantifications of the ratio of the intron 9 and synthetic poly(A) signals are shown as the mean ± S.E. from three independent experiments.