Like vertebrate FS proteins, dFS is subdivided into a N-terminal domain (N) and three FS domains (FS1-3). In contrast to its vertebrate orthologues, dFS encodes an unusually long signal peptide trailer, which contains three potential transmembrane domains (84-104, 161-180, 194-211), and a 260 amino acid insertion in FS1, which adds to the overall positive charge of the protein. In this study, we use a truncated cDNA that encodes a shorter signal leader that starts after amino acid 62. The location of the HA and RGS-6His tags in the constructs used in this study are indicated on top. In the absence of protein modifications, the predicted sizes of the signal leader and the processed full-length secreted form are 16 kD and 62 kD respectively.