Figure 1. CERKL isoform structure. A: The diagram shows the genomic exon-intron structure of the CERKL gene with the initiation and stop codons. The position of the nonsense mutation (R257X) identified in RP families as well as the splicing junctions resulting in isoforms a, b, c, and d are indicated. Asterisks indicate the position of the rare GC-splicing donor sites. B: The mature CERKL mRNA isoforms, indicating the relative position of the encoded DAG kinase and putative PH domains, are depicted. Note that exon 4b (isoform b, in gray) is located well within the DAG kinase domain, while isoforms c and d lack this domain. Grey small double arrows indicate the position of the primers used for specific isoform RT–PCR analyses (see Methods). The figure is drawn to scale except for the introns depicted with a broken line.