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

Golgi (Kexlp) are not always in mutually exclusive cisternae and their intracellular distribution may partially overlap. This can be the case in mammals where a pair of trans-Golgi and medial-Golgi glycosyltransferases showed substantial overlap (Nilsson et al., 1993) . The Kre2p/Mnnlp compartment remains to be precisely defined but some evidence suggests it could be identical to, or overlap with, compartments containing the Golgi type II membrane N-glycoprotein guanosine diphosphatase, Gdalp (Abeijon et al., 1989 (Abeijon et al., , 1993 . Subcellular fractionation experiments indicated that Gdalp and Kre2p activities cosediment (Abeijon et al., 1989) , whereas Gdalp and the late Golgi marker, Kex2p, are in distinct compartments (Bowser and Novick, 1991) . Mnnlp also cosediments with Gdalp and was found in fractions different from those containing Kex2p . These results are in accord with our immunofluorescence data indicating that Kre2p and Mnnlp are in the same Golgi compartment.