Coding potential of the novel mRNA species encoding Rex-protein isoforms. a Schematic representation of 1-2-3, 1-2-3a, 1-2-C and 1-2-Ca mRNAs; start and stop codons are indicated by arrows. Coloured boxes (not in scale) indicate the amino acid sequences differing in the alternatively spliced mRNAs. b Predicted amino acid sequences of proteins coded by the x-III ORF in the different mRNAs. Amino acid sequences are indicated in colours matching the boxes indicated in a.