title: The Golgi-localization of yeast Emp47p depends on its di-lysine motif but is not affected by the ret1-1 mutation in alpha-COP.
abstract: The Saccharomyces cerevisiae EMP47 gene encodes a nonessential type-I transmembrane protein with sequence homology to a class of intracellular lectins defined by ERGIC-53 and VIP36. The 12-amino acid COOH-terminal cytoplasmic tail of Emp47p ends in the sequence KTKLL, which conforms with the consensus for di-lysine-based ER-localization signals. Despite the presence of this motif, Emp47p was shown to be a Golgi protein at steady-state. The di-lysine motif of Emp47p was functional when transplanted onto Ste2p, a plasma membrane protein, conferring ER localization. Nevertheless, the di-lysine motif was required for Golgi-localization of Emp47p and showed the same charge-independent, position-dependent characteristics of other di-lysine motifs. Alpha-COP has been shown to be required for ER localization of di-lysine-tagged proteins. Consistent with this finding, the Ste2p-Emp47p hybrid protein was mislocalized to the cell surface in the alpha-COP mutant, ret1-1. Surprisingly, the Golgi-localization of Emp47p was unaffected by the ret1-1 mutation. To investigate whether Emp47p undergoes retrograde transport from the Golgi to the ER like other di-lysine-tagged proteins we developed an assay to measure this step after block of forward transport in a sec12 mutant. Under these conditions retrograde transport led to a specific redistribution of Emp47p from the Golgi to the ER. This recycling occurred from a Golgi subcompartment containing alpha 1,3 mannose-modified oligosaccharides suggesting that it originated from a medial-or later Golgi compartment. Thus Emp47p cycles between the Golgi apparatus and the ER and requires a di-lysine motif for its alpha-COP-independent, steady state localization in the Golgi.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D020756:Coatomer Protein; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism; D005656:Fungal Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D006056:Golgi Apparatus / Q000737:chemistry*; D037102:Lectins / Q000737:chemistry / Q000235:genetics; D008239:Lysine / Q000032:analysis; D008358:Mannose / Q000378:metabolism; D037241:Mannose-Binding Lectins; D008364:Mannosyltransferases / Q000032:analysis; D008565:Membrane Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions; D033921:Vesicular Transport Proteins
chemical_list: D020756:Coatomer Protein; C096914:EMP47 protein, S cerevisiae; D005656:Fungal Proteins; D037102:Lectins; D037241:Mannose-Binding Lectins; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D008364:Mannosyltransferases; D008239:Lysine; D008358:Mannose