Rab GTPases control transport between the ER and the Golgi complex and, consequently, are important for maintenance of the Golgi. GTPase-activating proteins (GAPs) inactivate GTP-bound Rab proteins; so to discover which human Rab proteins are needed to maintain an active Golgi complex, Francis Barr and colleagues have screened a host of human Rab GAPs for the ability to disrupt the Golgi and ER-to-Golgi protein transport in human cells (see ). They find that only two GAPS (RN-tre and TBC1D20, GAPS for Rab43 and Rab1, respectively) disrupt both these processes. TBC1D20, the authors show, is localised to the ER by a transmembrane anchor and its overexpression blocks ER-to-Golgi transport and causes loss of the Golgi. Knocking down Rab1 by RNAi produces a similar phenotype, they report, whereas expression of the TBC1D20-binding partner reticulon antagonises the effects of TBC1D20 overexpression. The authors therefore conclude that Rab1 and Rab43 are required for the biogenesis and maintenance of human Golgi complexes.
