Figure 3

Alu insertions into an exon activate intronization in the CWF19L1 gene. (a) Intronization. (i) Illustration of the last exon of the CWF19L1 gene in mouse. (ii) During primate evolution, two Alu elements were inserted into the exon. (iii) Because of these insertions, an intronization process activates two splice sites within the exon, a 3' and a 5' splice site. The isoform in which the intron is spliced out is supported by 12 mRNA/expressed sequence tags (ESTs), and the isoform in which the intron is retained is supported by four mRNA/ESTs. (b) Testing the splicing pathway of this exon between human and mouse. Polymerase chain reaction (PCR) analysis on normal cDNAs from human kidney (marked H) and from mouse brain tissue (marked M). PCR products were amplified using species-specific primers, and splicing products were separated in 1.5% agarose gel and sequenced. (c) Alignment of the sequence of the last exon of the CWF19L1 gene among human, mouse, rat, and dog is shown. The two Alu elements are marked in gray. The selected 5'ss and 3'ss are marked.