Levels of Alu-exon inclusion and RNA editing in the endogenous human NARF gene. (a) cDNAs from various normal human tissues or cDNAs from various cell-lines were PCR amplified using primers specific for the two exons flanking the exonized Alu (upper and lower panels, respectively). The inclusion level of the Alu-exon is indicated at the top of the panel, and represents the total percentage of the Alu-containing mRNA isoform, where 100% corresponds to the total of both mRNA isoforms (inferred by the ImageJ program). Each PCR product was confirmed by sequencing. Schemata of the two mRNA products are shown on the right. (b) Editing efficiency in the five exonic sites (E1, E2, E3, E4 and E5; see Figure 1 for site positions) in different tissues and cell lines. The editing frequencies in each of the five edited sites, derived from sequence results obtained from an average of three independent amplifications, were quantified using the Discovery Studio Gene 1.5 program.