Localization of the Lys, Asp, Glu, Leu tetrapeptide receptor to the Golgi complex and the intermediate compartment in mammalian cells

An analysis of the localization of the KDEL receptor is complicated by the difficulty of defining the precise boundary between the rough ER and the beginning of the Golgi complex, which we operationally define as the compartment where the Golgi mannosidase I (Man I) functions. One useful way of defining this boundary in a functional sense is the 15°C block (Saraste and Kuismanen, 1984) that inhibits the entry of newly synthesized membrane proteins from the ER into the Man I compartment (Balch et al., 1986) . Within this framework one can now identify two distinct compartments through which proteins must pass before entry into the Golgi complex. The first is the rough ER itself, the site of synthesis, and the second is the organelle that is now generally referred to as the intermediate compartment (IC) (Hauri and Schweizer, 1992; Lippincott-Schwartz, 1993) .