The PKD1 family of proteins as exemplified by the 10 SpREJs and five hPKD1 protein architectures. The predicted secondary structures are shown. Domain boundaries were taken from the Pfam database. The REJ domain is split into two sections in SpREJ7 and partial REJ domains occur in SpREJ8 and 9, and hPKD1L2. hPKD1L3 does not contain a REJ domain. Most of these predicted structures show a GPS domain upstream of transmembrane helix 1 (TM1) and a PLAT/LH2 domain immediately after the first TM.