The YPT Gene Family of Schizosaccharomyces Pombe
The ypt/rab family is a group of related proteins within the ras superfamily of small GTP-binding proteins. The original members of the group, Ypt1 and Sec4, were identified in the budding yeast Saccharomyces cerevisiae, where they appear to function at different stages of the secretory pathway, namely traffic from the endoplasmic reticulum to the Golgi complex and from the Golgi complex to the plasma membrane respectively 1,2. From these observations arose the hypothesis that the protein family may play a general role in eukaryotic membrane traffic, with a different member of the family determining the specificity of fusion of each class of vesicle mediating transport between the different compartments in the cell2. Consistent with this hypothesis, members of the family (known as rab proteins) have been identified in mammalian cells3,4,5 and in several cases the proteins have been shown to localise to different intracellular compartments6,7,8. In two cases the proteins localise to distinct populations of endosomes6, suggesting that the rab family is involved in endocytic as well as exocytic processes. Indeed, convincing evidence has been provided that the rab5 protein is directly involved in endosome fusion9. Except where such cell-free assays are available, however, it is difficult to determine the function of the mammalian proteins, since the genetic methods used in budding yeast are not generally applicable.
KeywordsFission Yeast Golgi Complex Schizosaccharomyces Pombe Keyhole Limpet Haemocyanin Tetramethyl Ammonium Chloride
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