MULTI-PROTEIN COMPLEXES IN THE CIS GOLGI OF SACCHAROMYCES-CEREVISIAE WITH ALPHA-1,6-MANNOSYLTRANSFERASE ACTIVITY

Anp1p, Van1p and Mnn9p constitute a family of membrane proteins requir ed for proper Golgi function in Saccharomyces cerevisiae. We demonstra te that these proteins colocalize within the cis Golgi, and that they are physically associated in two distinct complexes, both of which con tain Mnn9p, Furthermore, we identify two new proteins in the Anp1p-Mnn 9p-containing complex which have homology to known glycosyltransferase s. Both protein complexes have alpha-1,6-mannosyl-transferase activity , forming a series of poly-mannose structures, These reaction products also contain some alpha-1,2-linked mannose residues, Our data suggest that these two multi-protein complexes are responsible for the synthe sis and initial branching of the long alpha-1,6-linked backbone of the hypermannose structure attached to many yeast glycoproteins.