SCRAMBLED EXONS

Using a sensitive assay for RNA expression, we identified several abnormally spliced transcripts in which exons from a candidate tumor suppressor gene (DCC) were scrambled during the splicing process in vivo. Cloning and sequencing of PCR-amplified segments of the abnormally spliced transcripts showed that exons were joined accurately at consensus splice sites, but in an order different from that present in the primary transcript. Four scrambled transcripts were identified, each involving a different pair of exons. The scrambled transcripts were found at relatively low levels in a variety of normal and neoplastic cells of rodent and human origin, primarily in the nonpolyadenylated component of cytoplasmic RNA. These results demonstrate that the splicing process does not always pair sequential exons in the order predicted from their positions in genomic DNA, thus creating a novel type of RNA product.