THE HUMAN DYSTROPHIN GENE REQUIRES 16 HOURS TO BE TRANSCRIBED AND IS COTRANSCRIPTIONALLY SPLICED

The largest known gene is the human dystrophin gene, which has 79 exon s spanning at least 2,300 kilobases (kb). Transcript accumulation was monitored from four regions of the gene following induction of express ion in muscle cell cultures. Quantitative reverse transcription-polyme rase chain reaction (RT-PCR) results indicate that approximately 12 h are required for transcription of 1,770 kb (at an average elongation r ate of 2.4 kb min(-1)), extrapolating to a transcription time of 16 h for the complete gene. Accumulation profiles for spliced and total tra nscript demonstrated that transcripts are spliced at the 5' end before transcription is complete providing strong evidence for cotranscripti onal splicing. The rate of transcript accumulation was reduced at the 3' end of the gene relative to the 5' end, perhaps due to premature te rmination of transcription complexes.