Identification and characterization of a lower plant Ypt/Rab guanosine dissociation inhibitor (GDI).

The cDNA encoding a Ypt/Rab guanosine dissociation inhibitor (Ypt-GDI) was isolated from the multicellular green alga Volvox carteri, representing the first complete plant gdi gene described. The gdiV1 gene occurs as a single copy in the algal genome, indicating that its product regulates all YptV proteins from Volvox. The derived GDI protein (GDIV1p) shows high similarity to animal and fungal GDIs. A specific antibody developed against GDIV1p detected the protein throughout the whole Volvox life-cycle. GDIV1p was localized in the cytoplasm and in the algal flagellum. This is in line with earlier findings of a dual localization of Ypt proteins both in the cell body and in the motility organelle, and indicates a novel role of the GDI/Ypt system, possibly in intraflagellar transport.