Fig. 1. Structure of the cca-1 gene and CCA-1 calcium channel. (A) Intron-exon structure of cca-1. Coding exons are represented by filled rectangles, non-coding exons by open rectangles. The ad1650 and gk30 deletions are indicated by bars. All cDNAs characterized were found to be trans-spliced at the 5' end to the SL1 leader RNA (SL1). The most-abundant transcript, cca-1A, is composed of all exons except exon 19. Splice variant cca-1B uses an alternative splice donor in exon 18, which is spliced to exon 19. The cca-1D transcript splices exon 17 directly to exon 19. The inclusion of exon 19 would add amino acid residues to the pore loop region of domain II, and may have significant effects on the activity of the channel. Splice variant cca-1C uses an alternative 5' splice donor for exon 24, which is predicted to result in the incorporation of an additional 15 amino acids in the III-IV loop. Sequences of the four splice variants have been submitted to GenBank under accession numbers AY313898 (cca-1A), AY313899 (cca-1B), AY313900 (cca-1C) and AY322480 (cca-1D). The PCR products used to generate the cca-1::GFP fusion constructs are diagrammed and labeled with the names of the primers used for amplification (cca35/40 and cca38/34). (B) Domain structure of CCA-1. Open cylinders indicate transmembrane domains, and the positions of the alternative exons found in splice variants B, C and D are shown.