PROTEIN RETENTION IN THE ENDOPLASMIC-RETICULUM OF INSECT CELLS IS NOTCOMPROMISED BY BACULOVIRUS INFECTION

High level expression of the major auxin-binding protein (ABP1) from m aize (Zea mays L.) has been used to demonstrate that the machinery for retaining proteins in the endoplasmic reticulum (ER) of insect cells functions efficiently throughout the baculovirus infection cycle. Immu nolocalization showed wild-type ABP1 (ABP1-KDEL) to be targeted to the lumen of the ER, in accordance with its signal peptide and carboxyter minal KDEL ER-retention signal, The protein accumulated in dilations o f the ER, and none was detected at the cell surface. Immunoblotting of concentrated culture medium confirmed that ABP1-KDEL was not secreted at a detectable level. In contrast, when the carboxyterminus was muta ted to KEQL, secretion of the baculovirus-expressed protein was readil y detected, Immunolocalization and immunoblotting demonstrated that a high proportion of the ABP1-KEQL protein was secreted at the cell surf ace and into the culture medium, The data demonstrate that the ER of i nsect cells has a great capacity to retain proteins and that this prop erty is largely unaffected by the cellular disruption caused by baculo virus replication. (C) 1996 Academic Press Limited