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

Second, Chapman and Munro (1994) reported that a Pho8 chimeric protein containing a Kre2p TMD (chimeric protein PKP) slowed vacuolar processing of the luminal portion of Pho8p. They inferred from their results that PKP was at least partially localized in the Golgi complex and was retained by the Kre2p TMD. Again, the PKP chimeric protein was not localized intracellularly. This is clearly different from our results with Pho8p chimeras, which show that the Kre2p cytoplasmic NHz-terminal and transmembrane domains (KKP) are not sufficient for proper Golgi retention and the presence of the Kre2p cytoplasmic tail, TMD, and stem region is required for full retention of a Pho8p reporter protein (KKKP) in the yeast Golgi. To resolve this apparent inconsistency, we obtained the PKP construct and, on examination of its cellular location, found that it was exclusively localized to the vacuole displaying no punctiform fluorescence (data not shown). This finding is entirely consistent with our localization results with KKP, and offers no support for the Chapman and Munro conclusion that the Kre2p TMD will at least partially retain a heterologous protein in the yeast Golgi.