Localization and targeting of the Saccharomyces cerevisiae Kre2p/Mnt1p alpha 1,2-mannosyltransferase to a medial-Golgi compartment

Consistent with this assignment, previous biochemical studies provide evidence that Kre2p is localized in a compartment distinct from the late Golgi. Immunoisolated late Golgi organelles containing the endoproteinases Kexlp, Kex2p, and DPAP A were shown to be devoid of Kre2p (Bryant and Boyd, 1993) . Our immunocytochemical colocalization results also indicate that Kre2p is not in the same compartment as Kexlp. The 35% of Kre2p and Kexlp punctiform fluorescence signals that do colocalize could be due to two or more stacked cisternae that are seen in ~40% of all cisternae in a given yeast cell (Preuss et al., 1992) . However, the possibility remains that proteins from the medial-Golgi (Kre2p) and from the late