Small GTP-Binding Proteins are Associated with the Vesicles That are Targeted to Vacuoles in Developing Pumpkin Cotyledons : GROWTH AND DEVELTOPMENT : PROTEINS, ENZYMES AND METABOLISM

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Dense vesicles mediate the final step in the delivery of seed proteins to vacuoles in developing pumpkin (Cucurbita sp.) cotyledons. To explore the vesicle-mediated transport system that is targeted to vacuoles in plant cells, we isolated the dense vesicles and examined then for the presence of guanine nucleotide-binding proteins. GTP-binding proteins of 25 kDa and 27 kDa were detected on the isolated vesicles. The 25-kDa protein had dithiothreitol-dependent GTP-binding activity, but binding of GTP by the 27-kDa protein showed no such dependence. Binding of [α-^<32>P]GTP to these proteins was completely prevented by a 100-fold molar excess of unlabeled GTP or GDP, whereas ATP, CTP and UTP each had no effect on the binding. The GTP-binding proteins were not extracted from the vesicles by solutions of 1 M NaCl, 5 M urea or 0.1 M Na_2CO_3, but they could easily be extracted by solutions of 1 % sodium cholate or 1% Triton X-100, an indication that these proteins are associated with the membrane of the vesicles. These results suggest that two different small GTP-binding proteins might function in the targeting and/or fusion of the vesicles to the vacuolar membranes or in the budding of the vesicles.
日本植物生理学会の論文