Characterization of the unprocessed and processed forms of rab6 expressed in baculovirus/insect cell systems

Rab6 protein (rab6p) belongs to a family of ras-like GTP-binding proteins thought to be involved in the regulation of intracellular transport in mammalian cells. We have constructed a recombinant baculovirus in order to express rab6p in insect cells. We report here the characterization of four forms of this protein which are found in cytosolic and membrane fractions of infected Sf9 cells. The two major forms are a cytosolic 24 kD protein which represents the unprocessed precursor form of rab6p and a membrane-bound isoprenylated 23 kD protein which represents the processed form. Two other minor forms were also detected: a cytosolic isoprenylated 23 kD protein which may represent a pool in equilibrium with the 23 kD membrane-bound form and a 24 kD non-isoprenylated membrane-bound form which may represent an intermediate in the processing of rab6p.