Abstract
Protein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins. Proteins enter the ER by the Sec61 translocon, a proteinaceous channel composed of three subunits, alpha, beta and gamma. While it is known that Sec61alpha forms the actual channel, the function of the other two subunits remains to be characterized.In the present study we have investigated the function of Sec61beta in Drosophila melanogaster. We describe its role in the plasma membrane traffic of Gurken, the ligand for the Epidermal Growth Factor (EGF) receptor in the oocyte. Germline clones of the mutant allele of Sec61beta show normal translocation of Gurken into the ER and transport to the Golgi complex, but further traffic to the plasma membrane is impeded. The defect in plasma membrane traffic due to absence of Sec61beta is specific for Gurken and is not due to a general trafficking defect.Based on our study we conclude that Sec61beta, which is part of the ER protein translocation channel affects a post-ER step during Gurken trafficking to the plasma membrane. We propose an additional role of Sec61beta beyond protein translocation into the ER.
