title: Nested introns in an intron: evidence of multi-step splicing in a large intron of the human dystrophin pre-mRNA.
abstract: The mechanisms by which huge human introns are spliced out precisely are poorly understood. We analyzed large intron 7 (110199 nucleotides) generated from the human dystrophin (DMD) pre-mRNA by RT-PCR. We identified branching between the authentic 5' splice site and the branch point; however, the sequences far from the branch site were not detectable. This RT-PCR product was resistant to exoribonuclease (RNase R) digestion, suggesting that the detected lariat intron has a closed loop structure but contains gaps in its sequence. Transient and concomitant generation of at least two branched fragments from nested introns within large intron 7 suggests internal nested splicing events before the ultimate splicing at the authentic 5' and 3' splice sites. Nested splicing events, which bring the authentic 5' and 3' splice sites into close proximity, could be one of the splicing mechanisms for the extremely large introns.
authors: School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292, Japan. suzuki-h@jaist.ac.jp
authors: Hitoshi
authors: H
authors: Suzuki
authors: Toshiki
authors: T
authors: Kameyama
authors: Kenji
authors: K
authors: Ohe
authors: Toshifumi
authors: T
authors: Tsukahara
authors: Akila
authors: A
authors: Mayeda
mesh_terms: D016189:Dystrophin / Q000235:genetics* / Q000378:metabolism; D005095:Exoribonucleases / Q000378:metabolism; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D012322:RNA Precursors / Q000235:genetics* / Q000378:metabolism; D022821:RNA Splice Sites; D012326:RNA Splicing; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D016189:Dystrophin; D012322:RNA Precursors; D022821:RNA Splice Sites; D005095:Exoribonucleases; C080868:ribonuclease R