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Small GTPases of the Rab family are key regulators of membrane trafficking. Each Rab shows a characteristic subcellular distribution, and may serve as an important determinant of organelle identity. The molecular mechanisms responsible for targeting Rabs to specific intracellular compartments, however, remain poorly understood. The divergent C-terminal hypervariable region was postulated to contain Rab targeting information. We generated a series of hybrid Rab proteins by exchanging the hypervariable domains of Rab1a, Rab2a, Rab5a, Rab7 and Rab27a, and analysed their subcellular localisations. We found that the various hybrid proteins retained their targeting to the parent organelle and were functionally active. We conclude that the hypervariable region does not contain a general Rab targeting signal. Furthermore, we identified other regions within the RabF and RabSF motifs that are required for …