Exon trapping: A genetic screen to identify candidate transcribed sequences in cloned mammalian genomic DNA

Identification and recovery of transcribed sequences from cloned mammalian genomic DNA remains an important problem in isolating genes on the basis of their chromosomal location. We have developed a strategy that facilitates the recovery of exons from random pieces of cloned genomic DNA. The basis of this 'exon trapping' strategy is that, during a retroviral life cycle, genomic sequences of nonviral origin are correctly spliced and may be recovered as a cDNA copy of the introduced segment. By using this genetic assay for cis-acting sequences required for RNA splicing, we have screened ≃20 kilobase pairs of cloned genomic DNA and have recovered all four predicted exons.