Characterization of Cop I coat proteins in plant cells

Membrane traffic in eukaryotic cells is mediated by COP (coat protein)-coat ed vesicles. Their existence in plant cells has not yet been unequivocally demonstrated, although coated vesicles (probably with a COP coat) can be se en by electron microscopy, At the gene level, plant cells seem to contain a ll the components necessary to form COP-coated vesicles. In this paper, we have used antibodies raised against mammalian COPI coat proteins to detect putative homologues in rice (Oryza sativa) cells. Using these antibodies, w e have found that rice cells contain alpha-, beta-, beta'-, and gamma-COP, as well as ADP-ribosylation factor (ARF) 1 protein. In addition, we show th at antibodies against mammalian beta'-COP can immunoprecipitate not only be ta'-COP but also alpha-, beta-, and gamma-COP, suggesting that COPI compone nts in rice cells exist as a complex (or coatomer) in the cytosol, as in ma mmalian cells. Finally, we show that COP binding to membranes is GTP-depend ent, and that ARF1 also binds to membranes in a GTP-dependent manner. (C) 2 000 Academic Press.