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

To attempt to define in which Golgi compartment Kre2p is localized, its intracellular localization was compared with that of a known medial-Golgi protein, the mannosyltransferase Mnnlp (Ballou, 1990; Graham et al., 1994; Yip et al., 1994) , by double-label immunofluorescence (Fig. 5) . Quantitative evaluation of punctate spot distribution (described in Materials and Methods) revealed that 75% of the Kre2p corresponding Texas red-labeled structures coincided with the FITC-labeled Mnnlp fluorescence spots. The location of Kre2p was also compared with that of a late Golgi protein, the carboxypeptidase Kexlp (see Figs. 2 and 5; Dmochowska et al., 1987; Bussey, 1989, 1992) . A quantitative scoring of punctiform fluorescence distribution indicated that 65% of the Kre2p corresponding structures did not coincide with the Kexlp fluorescence patches.