Required for protein secretion (PubMed:16452979, PubMed:23369713). May participate in cargo loading by binding to COPII coat subunits and guiding SH3-bound proteins into a growing carrier (PubMed:16452979). At basal transitional ER sites in follicle epithelial cells, mediates the exit of basal membrane protein such as vkg, LanB1 and Trol, from the endoplasmic reticulum (ER) to basal Golgi clusters (PubMed:23369713). RNAi-mediated knockdown results in basal membrane proteins such as vkg, LanB1 and Trol accumulating in the basal ER. Belongs to the MIA/OTOR family. Tango1 subfamily. Truncated N-terminus. Deletion of 12 residues at position 1268 causing a frameshift. Deletion of 172 residues at position 924.