Tissue-specific splicing in vivo of the beta-tropomyosin gene: dependence on an RNA secondary structure.

The beta-tropomyosin gene in chicken contains two mutually exclusive exons (exons 6A and 6B) which are used by the splicing apparatus in myogenic cells, respectively, before (myoblast stage) and after (myotube stage) differentiation. The myoblast splicing pattern is shown to depend on multiple sequence elements that are located in the upstream intron and in the exon 6B and that exert a negative control over exon 6B splicing. This regulation of splicing is due, at least in part, to a secondary structure of the primary transcript, which limits in vivo the accessibility of exon 6B in myoblasts.