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

Protein 4.1 pre-mRNA splicing is regulated in tissue- and development-specific manners. Exon 16, which encodes the N-terminal region of the spectrin/actin-binding domain, is one of the alternatively spliced sequence motifs. It is present in late differentiated erythroid cells but absent from early erythroblasts and from lymphoid cells. We describe a single nucleotide deletion of the erythroid protein 4.1 gene associated with hereditary elliptocytosis. 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 premature 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 stop codon does not affect the tissue-specific alternative splicing among the two cell types analyzed and that the resulting alteration of mRNA metabolism correlates with the retention of exon 16 in reticulocytes. Conversely, skipping of exon 16 in lymphoid cells converts the mutant mRNA to a normal lymphoid-specific mRNA isoform, hence bypassing the nonsense codon. Consistent with data obtained on constitutive nonsense exons, our observations argue in favor of a stop codon recognition mechanism that occurs after the regulated splicing status of the nonsense exon has been achieved.