Molecular cloning and characterization of a Pichia pastoris ortholog of the yeast Golgi GDP-mannose transporter gene

There are two structural profiles in the yeast Golgi. The Golgi of Saccharomyces cerevisiae is composed of a number of vesicular compartments dispersed in the cytoplasm as recognized by a large number of Golgi marker proteins. In contrast, the Golgi of Pichia pastoris was reported to be organized in a small number of stacked cisternae located near the transitional endoplasmic reticulum (tER) sites by electron microscopy and immunofluorescent staining of a few marker proteins. The guanosine diphosphate (GDP)-mannose transporter (GMT) is an essential component in the yeast Golgi apparatus. We isolated an ortholog of the GMT gene of P. pastoris and visualized the gene product by epitope tagging to verify the structural characteristics of the Golgi. The tagged product in P. pastoris cell was observed in rod-like compartments in which Och1 mannosyltransferase was also found and the tER marker Sec12 and Sec13 proteins localized very close to them. The present results add further evidence of the restricted localization of the Golgi in P. pastoris cell.