ERP61 IS GRP58, A STRESS-INDUCIBLE LUMINAL ENDOPLASMIC-RETICULUM PROTEIN, BUT IS DEVOID OF PHOSPHATIDYLINOSITIDE-SPECIFIC PHOSPHOLIPASE-C ACTIVITY

Using antibody raised against putative Form I phosphatidylinositide-sp ecific phospholipase C (PI-PLC) and direct amino acid sequencing of th e protein recognized by this antibody, we have shown that the antibody reacts with luminal endoplasmic reticulum (ER) proteins, including ER p61. ERp61 possesses a COOH-terminal QEDL sequence that acts as an ER retention signal. Additional experiments have shown, however, that PI- PLC activity is separable from ERp61 and that rat or murine ERp61 expr essed in COS cells failed to produce an increase in PI-PLC activity in the COS cells. Finally, we have identified ERp61 as GRP58, a 58-kDa p rotein inducible by glycosylation block and treatment with the Ca2+ io nophore, A23187. (C) 1994 Academic Press, Inc.