A premature termination codon within an alternative exon affecting only the metabolism of transcripts that retain this exon

Protein 4.1 pre mRNA splicing is regulated in tissue and development specif ic manners. Exon 16, which encodes the N-terminal region of the spectrin/ac tin binding domain, is one of the alter natively spliced sequence motifs, I t is present in late differentiated erythroid cells but absent from early e rythroblasts and from lymphoid cells, We describe a single nucleotide delet ion of the erythroid protein 4.1 gene associated with hereditary elliptocyt osis. The deletion located in exon 16 leads to a frameshift and a premature termination codon within the same exon. In an effort to examine the premat ure stop codon effect in relationship with exon 16 alternative splicing, we analyzed erythroid and lymphoid protein 4.1 mRNAs using the mutation and a linked downstream polymorphism as markers. We found that the premature sto p codon does not affect the tissue-specific alternative splicing among the two cell types analyzed and that the resulting alteration of mRNA metabolis m correlates with the retention of exon 16 in reticulocytes. Conversely, sk ipping of exon 16 in lymphoid cells converts the mutant mRNA to a normal ly mphoid-specific mRNA isoform, hence bypassing the nonsense codon, Consisten t with data obtained on constitutive nonsense exons, our observations argue in favor of a stop codon recognition mechanism that occurs after the regul ated splicing status of the nonsense exon has been achieved, Hum Mutat 14:1 45-155, 1999, (C) 1999 Wiley-Liss, Inc.