Exon trapping is a technique for cloning exon sequences from genomic DNA by selecting for functional splice sites, relying on the cellular splicing machinery. The genomic DNA containing the putative exon(s) is cloned into an exon-trap vector, which has a promoter, polyadenylation signals, and splice sites, and then transfected into a cell line. If there are functional splice sites in the genomic DNA fragment, the segments of DNA between the splice sites will be removed. Total RNA is isolated and reverse-transcribed. After cDNA synthesis and PCR amplification, the exon of interest is cloned.