Retention of p63 in an ER-Golgi intermediate compartment depends on the presence of all three of its domains and on its ability to form oligomers

The only membrane protein characterized and cloned so far with a stable ER-Golgi intermediate localization is p63 (Schweizer et al., 1993a,b) . mAbs against p63 recognized an extended ER-Golgi intermediate membrane structure which indicated that the ERGIC may be larger than previously suggested by the ERGIC-53 analysis. Unlike ERGIG-53, the distribution of p63 was insensitive to organelle perturbants such as low temperature and brefeldin A (Schweizer et al., 1993a) . Sequence analysis together with biochemical data demonstrated that p63 is a nonglycosylated, reversibly palmitoylated type II transmembrane protein with a 106 amino acid NHe-terminal cytosolic tall, a single transmembrane domain, and a large extracytoplasmic domain of 474 amino acids (Schweizer et al., 1993a,b) .