Figure 2

Exon phasing of the CFTR gene (Universal Mutation Database [25]). The CFTR gene comprises 27 exons which were previously numbered 1–24 [23] with subdivisions A and B for exons 6, 14 and 17, recognized as distinct units after the initial publication of the gene (GenBank NM_000492.2). Here we presents the numerotation of CFTR exons as described in UCSC (University of California Santa Cruz) Human Genome databases and updated as March 2006 Assembly [24]. Each exon is presented as a blue box with the international numbering within the box, and the familiar numbering above it. Each extremity of the box represents the specific phasing of the exon. Left end of exons: 1) vertical extremity: the exon begins by the first nucleotide of a codon; 2) curve: the exon begins by the second nucleotide of a codon; 3) arrow: the exon begins by the third nuceotide of a codon. Right end of exons: 1) vertical extremity: the exon ends by the last nucleotide of a codon; 2) light blue curve: the exon ends by the first nucleotide of a codon; 3) arrow: the exon ends by the second nucleotide of a codon. Large-scale deletions can introduce a translational frameshift (and lead to a premature termination codon) when two exons are joined end to end (for example, exons 1 and 4). When two exons in the same phase are joined, it is assumed that no frameshift occurs and that a shorter protein with an internal deletion may be produced.