Structure of the hIL-5R minigene and PCR primer design.

(A) hIL-5Rα gene structure. The alternative splicing choice leading to the transcripts encoding the secreted or membrane-anchored isoforms is indicated by dashed lines. Exons are shown as boxes and are numbered on top, with exon 11 corresponding to the “soluble”-specific exon and exon 12 encoding the transmembrane region. Polyadenylation sites are shown below. (B) The 2 major transcripts from the hIL-5Rα gene. SOL encodes the major secreted variant; TM encodes the membrane-associated receptor.8 Boxes are translated regions, with protein domains shown: S indicates signal peptide; EC, extracellular domain; M, membrane anchor; C, cytoplasmic tail. (C) The structure of the minigenes. Boxes are translated regions, either from cDNA segments or from exons. (A)n is the polyadenylation site present in the “soluble”-specific exon; SV(A)n comes from SV40 and is artificially added. The position of the extra SV(A)n in pSV-MINI-2 is shown by a dashed line. The arrow represents the SV40 early promoter. On top, arrows indicate the positions of the primers used in the (competitive) RT-PCR experiments. Sizes of possible reaction products are indicated. Throughout the figure, black, gray, and hatched boxes correspond to exons, protein domains, or coding regions specifying the signal peptide, secreted isoform, or membrane-anchored isoform, respectively.