Dual targeting of Osh1p, a yeast homologue of oxysterol-binding protein, to both the Golgi and the nucleus-vacuole junction.
Oxysterol binding protein (OSBP) is the only protein known to bind specifically to the group of oxysterols with potent effects on cholesterol homeostasis. Although the function of OSBP is currently unknown, an important role is implicated by the existence of multiple homologues in all eukaryotes so far examined. OSBP and a subset of homologues contain pleckstrin homology (PH) domains. Such domains are responsible for the targeting of a wide range of proteins to the plasma membrane. In contrast, OSBP is a peripheral protein of Golgi membranes, and its PH domain targets to the trans-Golgi network of mammalian cells. In this article, we have characterized Osh1p, Osh2p, and Osh3p, the three homologues of OSBP in Saccharomyces cerevisiae that contain PH domains. Examination of a green fluorescent protein (GFP) fusion to Osh1p revealed a striking dual localization with the protein present on both the late Golgi, and in the recently described nucleus-vacuole (NV) junction. Deletion mapping revealed that the PH domain of Osh1p specified targeting to the late Golgi, and an ankyrin repeat domain targeting to the NV junction, the first such targeting domain identified for this structure. GFP fusions to Osh2p and Osh3p showed intracellular distributions distinct from that of Osh1p, and their PH domains appear to contribute to their differing localizations.
Levine
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TP
MRC Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom.
Munro
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D000818:Animals; D017487:Ankyrins / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D005838:Genotype; D006056:Golgi Apparatus / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000737:chemistry / Q000378:metabolism; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011987:Receptors, Steroid / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014617:Vacuoles / Q000378:metabolism; D000098825:Oxysterol Binding Proteins
D017487:Ankyrins; D002352:Carrier Proteins; D005656:Fungal Proteins; D008164:Luminescent Proteins; C432935:OSH2 protein, S cerevisiae; C432936:OSH3 protein, S cerevisiae; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins; C089501:SWH1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000098825:Oxysterol Binding Proteins; D049452:Green Fluorescent Proteins