Endoplasmic reticulum localization of Sec12p is achieved by two mechanisms: Rer1p-dependent retrieval that requires the transmembrane domain and Rer1p-independent retention that involves the cytoplasmic domain

In contrast, mannosyl modification of Dap2p is very fast (Fig. 8 B) . Dap2p appeared as the ll0-kD ER form containing 5--8 N-linked oligosaccharide chains and underwent further modification to the 120-kD mature (vacuolar) form during chase (Roberts et al., 1989) . Endo H treatment unveiled emergence of a smaller species, which is perhaps due to the degradation in the vacuole. Quantification of mannosyl modification indicates that 29% of Dap2p already acquired the ed---~6 mannosyl linkage during 10-min pulse, and the proportion increased to 70% at 60 min chase (see Table III ). The modification with etl---~3 linkage was also evident even at 0 min and extended during chase.